Skip to main content

Coronavirus Questions and Answers

Hopkins Experts Answer Your COVID-19 Questions


Have a question? Email us

Last updated May, 2022*

*Please note: This page is currently undergoing updates. Please visit the Centers for Disease Control and Prevention for the most up-to-date information on COVID-19.


Coronavirus and Variants: The Basics

What is a coronavirus?

Coronaviruses are a family of viruses that typically cause mild respiratory infections like the common cold, but also more severe (and potentially deadly) infections. They are zoonotic diseases, meaning they are transmitted from animals to people.

SOURCE: Global Health NOW

Why is it called a coronavirus?

Coronaviruses are named after the Latin word corona, meaning “crown” or “halo,” because they have “crown-like spikes on their surface,” according to the U.S. Centers for Disease Control and Prevention.

SOURCE: Global Health NOW

What severe diseases are caused by coronaviruses?

A coronavirus that originated in China led to the Severe Acute Respiratory Syndrome (SARS) outbreak in 2003. Another coronavirus emerged in 2012 in Saudi Arabia, causing Middle East Respiratory Syndrome (MERS).

SOURCE: Global Health NOW

What’s the difference between coronavirus, SARS-CoV-2, and COVID-19?

The novel coronavirus responsible for this outbreak is known as SARS-CoV-2. The illness caused by the virus is called COVID-19.

More information can be found here: Naming the coronavirus disease (COVID-19) and the virus that causes it—WHO.

SOURCE: Global Health NOW

Could COVID-19 or a variant have been here before January 2020?

The earliest recognized cases of COVID-19 in the United States date back to January 14, 2020. At the start of the epidemic in the US—January - March, 2020—there was limited testing capacity so most testing was done only on people with symptoms and some who had recently traveled to certain areas of the world. 

A recent study of antibodies found evidence of SARS-CoV-2 infections weeks prior to the first recognized cases. In this study, residents of 9 states had antibodies as early as mid-December, 2019. 

SOURCE: Keri Althoff and the National Institutes of Health

What symptoms do coronaviruses typically cause? How is COVID-19 different?

Common signs of coronavirus infection include runny nose, cough, fever, sore throat, and shortness of breath.

COVID-19 can cause a wide range of signs and symptoms at varying levels of severity. The most common are fever, dry cough, and tiredness. Other symptoms include shortness of breath or difficulty breathing, muscle aches, chills, sore throat, headache, or chest pain.

Other symptoms that aren’t as common include: gastrointestinal symptoms, new loss of smell or taste, skin changes (like lesions), confusion, and pink eye (conjunctivitis).

SOURCE: Mayo Clinic

Why does COVID-19 cause loss of smell?

Some patients can temporarily lose their sense of smell. This is because the “hook” of cells used by SARS-CoV-2 to latch onto and infect cells is up to 700 times more prevalent in the olfactory-supporting cells lining the inside of the upper part of the nose than in the cells lining the rest of the nose and windpipe that leads to the lungs. The supporting cells are necessary for the function/development of odor-sensing cells.


Why does COVID-19 cause shortness of breath?

COVID-19 can cause damage to the lungs that impedes their ability to remove oxygen from the air. A lot of patients develop what’s known as severe acute respiratory distress syndrome.

SOURCE: Jennifer Nuzzo

Does COVID-19 affect the heart?

One of the mechanisms that the SARS-CoV-2 virus uses to enter the lungs, called the ACE2 receptors, lives in the heart as well. When the virus enters the heart, it can cause clots, pulmonary embolism, or clots within the arteries of the heart causing a heart attack.

SOURCE: Public Health On Call

When and how should I seek medical attention?

Via the CDC:
If you develop any of the following emergency warning signs* for COVID-19, get medical attention immediately by calling your doctor’s office. Emergency warning signs include (but are not limited to):

  • Trouble breathing
  • Persistent pain or pressure in the chest
  • New confusion or inability to arouse
  • Bluish lips or face

Please call your medical provider for any other symptoms that are severe or concerning to you.

*This list is not all possible symptoms. Please call your medical provider for any other symptoms that are severe or concerning to you.


How are coronaviruses transmitted between people?

Although laboratory tests have shown that SARS-CoV-2 can remain on plastic and stainless steel for days, surfaces are not the main way that the virus spreads.

According to the WHO, the virus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak, sing, or breathe. Current evidence suggests that the virus spreads mainly between people who are in close contact with each other, typically within six feet such as at a "conversational distance." A person can be infected when aerosols or droplets containing the virus are inhaled or come directly into contact with the eyes, nose, or mouth.

The virus can also spread in poorly ventilated and/or crowded indoor settings, where people tend to spend longer periods of time. This is because aerosols remain suspended in the air and can travel farther than three feet.

Vaccination, wearing a mask, staying at least six feet away from others, and avoiding prolonged contact (more than fifteen minutes) indoors with others are all helpful mitigation factors.


When a person breathes in a droplet containing the SARS-CoV-2 virus, how long does it take for the virus to start binding to receptors in the nose and throat? Is it seconds, minutes, hours, or days?

[This probably occurs] within minutes to hours. It's probably not instantaneous. I'm sure in a petri dish or in a laboratory, it can be done in seconds. But in your human body, it's a little bit more complicated because there's mucus. There are little hairs on your cells that are constantly beating, trying to remove debris like viruses. So it's hard to know exactly what the time course is down to the precise unit of measurement.

SOURCE: Amesh Adalja

What's the difference between being asymptomatic and presymptomatic?

Asymptomatic individuals test positive for COVID-19 but “lack symptoms that would indicate SARS-CoV-2 infection.” Some people may not experience any symptoms during the entire course of their COVID-19 infection.

But some people may develop symptoms days after a positive test. These individuals would be classified as having been presymptomatic at the time of their positive test; they will eventually develop symptoms.

SOURCE: Johns Hopkins Bloomberg School of Public Health

When people are asymptomatic, can they spread the virus?

Yes. A lab study suggests that as many as 50% of people who have the disease show no symptoms and are still able to spread the disease.

SOURCE: Gigi Gronvall

How long is a person with an asymptomatic case shedding the virus?

Most people with COVID-19 can discontinue isolation 10 days after symptom onset. For people with no symptoms of COVID-19, isolation can be discontinued 10 days after the date of their first positive test.

Please note: This is an evolving situation and recommendations may change. For the latest, please check the CDC's site


If people are asymptomatic, how does the virus get from one person to another?

We now understand that the virus can be spread by people who have no symptoms at the time of transmission. Infected people can breathe out viral particles, which can infect others. Most documented transmission occurs over short distances, but some outbreaks have been reported where transmission occurred over a longer range. For this reason, experts caution about avoiding poorly ventilated indoor spaces, as these conditions may enable viral particles to build up and facilitate longer-range transmission.

Asymptomatic individuals test positive for COVID-19 but “lack symptoms that would indicate SARS-CoV-2 infection.” Some people may not experience any symptoms during the entire course of their COVID-19 infection.

But some people may develop symptoms days after a positive test. These individuals would be classified as having been presymptomatic at the time of their positive test; they will eventually develop symptoms.

Reviews have shown that most transmission from people who don’t have symptoms at the time of transmission occurs from people who turn out to be presymptomatic, not asymptomatic.

SOURCE: Jennifer Nuzzo

Is COVID-19 airborne?

The principal mode by which people are infected with SARS-CoV-2 is through exposure to respiratory fluids carrying infectious virus. Exposure occurs in three principal ways: inhalation of very fine respiratory droplets and aerosol particles; deposition of respiratory droplets and particles on exposed mucus membranes in the mouth, nose, or eye by direct splashes or sprays; and touching mucous membranes with hands that have been soiled either directly by virus-containing respiratory fluids or indirectly by touching surfaces with virus on them.

Enclosed spaces with inadequate ventilation or air handling, increased exhalation by an infectious person such as through physical exertion or raising their voice, and prolonged exposure can all contribute to a concentration of exhaled respiratory fluids, especially very fine droplets and aerosol particles that can build up in the air space. 


What is known about young children and COVID?

Young children can be infected and transmit to others. At this time, it appears that severe illness due to COVID-19 is uncommon among children. However, there is an urgent need to collect more data to assess the severity of illness related to new variants as well as the longer-term impacts of the pandemic on children, including ways the virus may harm the long-term physical health of children, as well as its emotional and mental health effects.

There is a rare and dangerous condition in sick children called multi-system inflammatory syndrome in children (MIS-C) which is thought to be caused by an immune reaction to SARS-CoV-2.

Children aged 5-11 are eligible for vaccination with a recommended Pfizer booster at 5 months past the last dose, and an additional primary dose for children with certain immunocompromised conditions.

SOURCE: Public Health On Call Podcast, CDC, American Academy of Pediatrics

Is COVID-19 worse than the flu?

For unvaccinated individuals, COVID-19 is much deadlier than the flu. COVID-19 has a higher severe disease and mortality rate than influenza in all age groups, except perhaps children under the age of 12.

COVID-19 vaccines provide substantial protection against hospitalization and death.

SOURCE: Andrew Pekosz

When can I resume normal activities after a COVID infection?

The CDC is monitoring the COVID-19 pandemic and has issued interim guidance for ending isolation. This guidance is subject to change so please check the CDC's site for the latest


What is the possibility of reinfection after you have recovered from COVID-19?

Based on what we know from similar viruses, some reinfections are expected. Ongoing studies will help us understand the likelihood of reinfection and how soon it can occur, who might be at higher risk, what reinfection means for immunity.

Certain variants, such as omicron, may be more likely to cause reinfection or breakthrough infections in vaccinated individuals. 

SOURCE: Public Health On Call Podcast, CDC, BMJ

Is there evidence of a heightened risk to pregnant women?

Pregnant people are at an increased risk for severe illness from COVID-19 compared to non-pregnant people. Having certain underlying medical conditions and other factors, including age, can further increase a pregnant or recently pregnant person’s risk for developing severe illness.

Pregnant people with COVID-19 are also at increased risk for preterm birth (delivering the baby earlier than 37 weeks) and might be at increased risk for other poor pregnancy outcomes.

Pregnant and recently pregnant and breastfeeding people can receive a COVID-19 vaccine. 

Learn more about newborns and COVID-19 here


What exactly are SARS-CoV-2 variants of concern and variants of interest? 

Because so many SARS-CoV-2 variants have emerged, the WHO has instituted a system to classify them into two major groups: Variants of Concern (VOCs) and Variants of Interest (VOI). VOCs are variants that have clearly shown the ability to transmit more easily in humans, evade vaccine, or cause increased disease severity. VOIs are variants that have mutations that might make them more of a threat to humans, but the data has either not been collected or is inconclusive. There are many variants that don’t fall into either of these categories because viruses like SARS-CoV-2 tends to mutate at a frequent rate, but most of those mutations don’t affect how the virus circulates or causes disease.

The WHO made a new naming system for VOCs and VOIs that uses Greek letters in place of the formal scientific designation or place of identification of these variants. For example, the alpha variant used to be referred to as “UK variant” or “B.1.1.7” and the delta variant was the “India variant” or “B.1.617.2”. 

SOURCE: Andrew Pekosz

Why are some variants of SARS-CoV-2 more transmissable? 

There are currently two theories about what, specifically, makes some of these variants more transmissible. One is that variant viruses are “stickier,” meaning it requires a smaller amount of virus to cause infection because it’s better at adhering to your cells. Another theory is that variants causes people to harbor more virus particles in their noses and throats, which means more virus is expelled when people talk, cough, or sneeze.

With omicron, there was a large number of mutations that occurred in the spike protein—the protein the virus uses to bind to and enter cells—which is the target of the vaccine. Those mutations look like they might allow the virus to escape from vaccine-induced immunity to some degree, allow the virus to bind more tightly to cells, and allow the virus to enter cells faster.

Behavioral and situational factors could help a more transmissible variant spread even further, but wearing a mask, ensuring physical distance, and hand washing will still help.

SOURCE: Public Health On Call, Andrew Pekosz

Is there a difference between "more transmissable" and "more contagious?"

Transmission is often used when we talk about populations, while contagious is more often used when we are talking about an individual. They are interchangeable to some degree.

SOURCE: Andrew Pekosz

Is there any change in guidance for how to protect yourself and others from new variants of SARS-CoV-2? 

Well-fitted masks properly worn, social distancing, and hand washing should work against the variants just as well. 

Most importantly, COVID-19 vaccines—and in particular the mRNA vaccines—are showing good protection against the VOCs, so go and get your COVID-19 vaccine!

SOURCE: Andrew Pekosz, CDC

How common is it for a virus to mutate? Is it unusual to see new variants of SARS-CoV-2 take hold this soon?

All viruses mutate, and SARS-CoV-2 has been mutating at a pretty consistent rate since it entered the human population. 

Omicron has accumulated an extremely large number of mutations compared to other lineages. Usually we can follow the evolution of a virus because we find related viruses with fewer mutations. But with this virus, it seems to have just appeared with a lot of mutations. 

SOURCE: Andrew Pekosz, The Hub


Are some groups at a higher risk for severe COVID-19 illness?

Severe illness from COVID-19 can include: hospitalization, intensive care, a ventilator to help with breathing, or death.

Being unvaccinated substantially increases everyone's risk of severe COVID. Additionally, available information suggests that the following are at a higher risk for severe illness from the virus:

  • Older adults:
    • More than 80% of COVID deaths occur in people over age 65
  • Many racial and ethnic minority groups and people with disabilities (due to long-standing systemic health and social inequities)
    • Studies have shown that people from racial and ethnic minority groups are also dying from COVID-19 at younger ages
  • People of any age with the following conditions:
    • Cancer
    • Chronic kidney disease
    • COPD
    • Immunocompromised state from solid organ transplant
    • Obesity (BMI of 30 or higher)
    • Pregnancy
    • Serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies
    • Sickle cell disease
    • Type 2 diabetes mellitus

Adults of any age with underlying medical conditions are at increased risk for severe illness. COVID-19 vaccines are recommended for and can be administered to most people with underlying medical conditions. In some cases, people with certain medical conditions that cause a suppressed immune system should receive a third dose of either the Moderna or Pfizer vaccine as soon as 28 days after the second dose. 

For a full list and recommended precautions, please visit the CDC resource.

SOURCES: CDC, Johns Hopkins Medicine

Do high-risk patients ever have mild coronavirus, or is it always the case that people who are at higher risk get very sick?

Certainly, people of advanced age and people with underlying conditions statistically are among those mostly likely to be hospitalized and die, but that’s not always the case. People in both of those categories also may have mild infection or may become sick and survive their illness.

SOURCE: Jennifer Nuzzo

Do we know, at this point, who is at risk of developing long COVID? 

At this point, there’s no data on who is more likely to get long COVID. 

It’s important to note that regardless of whether or not vaccines can help with symptoms, long-hauler COVID patients should get vaccinated for COVID. This will help prevent reinfection as we still don’t know how robust the immune response is in long-haul patients.

SOURCE: Gigi Gronvall

Can children develop long COVID? 

Recent data indicates that 2 - 10% of young COVID-19 survivors are estimated to experience lingering symptoms.

SOURCE: Hopkins Bloomberg Public Health Magazine

Are people on immunosuppressive drugs more susceptible to severe COVID-19?

New research finds that people taking immunosuppressive drugs to prevent organ transplant rejection or to treat inflammatory or autoimmune diseases do not fare worse than others on average when they are hospitalized with COVID-19. There is no indication that people taking these drugs should be concerned that their medication increases their risk for severe COVID-19.

COVID-19 vaccines are recommended for and can be administered to most people with underlying medical conditions. In some cases, people with certain medical conditions that cause a suppressed immune system should receive a third dose of either the Moderna or Pfizer vaccine as soon as 28 days after the second dose. 

SOURCES: Caleb Alexander, Johns Hopkins Bloomberg School of Public Health


What are all the different kinds of COVID tests?

Testing for COVID can be divided into two main groups: testing for active SARS-CoV-2 infection or testing for past SARS-CoV-2 infection. Active infection indicates that a person has virus that is replicating and that they could infect others. Past infection indicates that an individual has recovered from COVID-19 and has no actively replicating virus.

To test for active infection, diagnostic antigen or molecular tests are used. 

To test for past infection, serology tests are used. 

Learn more about the specific types of antigen, molecular, and serology tests, how they are collected, and when each should be used here

SOURCE: The Center for Health Security Testing Toolkit

What kind of COVID test should I get?

The Center for Health Security has created a flowchart to help you determine what COVID-19 test type you may need. 

In general, if you may have a current COVID-19 infection and you are experiencing symptoms, you should seek an antigen or molecular diagnostic test. These tests may be referred to with terms like: PCR, qPCR, rRT-PCR, antigen, rapid antigen test, RPA, RT-LAMP, and CRISPR.

SOURCE: The Center for Health Security

What's the difference between a rapid test versus a PCR test that takes 24 hours or longer?

PCR tests have to be done in the lab. That test has an amplification step so it can find small amounts of virus in somebody’s nose. 

The rapid antigen test requires a lot of virus to see a positive result because there’s no amplification step. The good part about that is that if you test positive in this fast test, then you really know you should not be around other people. You are infectious and need to isolate immediately.

There are pros and cons: you can catch an infection earlier with a PCR test, but you get the immediate actionable result with the rapid antigen test. 

SOURCE: Gigi Gronvall

How accurate are at-home COVID tests?

When used correctly, at-home rapid antigen tests are good at detecting high levels of the virus.

There is some data that at-home tests may not pick up infections from omicron as early as other variants, so if you feel symptoms but test negative you may need to test again and hold off a little bit on assuming that you're negative.

If you feel sick, however, you can't stop with a negative antigen test. It could be that your symptoms are driven by your immune system and that there's not [yet] enough virus in your nose to turn the test positive. Maybe a couple of days later, you do test positive once the virus gets to a higher level. It's not uncommon to have this kind of positive-negative issue because it has to do with the time course of infection. 

SOURCE: Gigi Gronvall, Amesh Adalja

If I test positive for COVID on an at-home test, what should I do? Is there anyone I need to call?

If you test positive using an at-home test, you should follow-up with your health care provider and follow the instructions on your test kit to report your results to the local health department. You should isolate in your home according to CDC guidelines and reduce contact with anyone living in your household.

After you’ve reported your results or spoken to your health care provider, you may be contacted by your local health department to alert any close contacts with whom you may have recently interacted. Always stay in touch with your health care provider, monitor your symptoms, and seek medical attention if necessary

SOURCE: Amanda Kobokovich

I got an antibody test after I got vaccinated and it came back negative. Does that mean the vaccine didn’t work for me?

Not all antibody tests are looking for the part of the virus that the vaccine is made from, so all that test was telling that person was that they never had COVID.

None of the tests right now are authorized to determine how well you responded to the vaccine. But the vaccines are really effective. If you indeed took the vaccine, you don’t need a test from your pharmacy to confirm you’re vaccinated.

SOURCE: Gigi Gronvall

Do different variants of SARS-CoV-2 affect testing accuracy?

Because of the diversity and breadth of tests currently available, most diagnostic tests can still be reliably used to diagnose the variant strains. 

SOURCE: The Center for Health Security

Prevention and Infection Control

How can I protect myself against coronaviruses?

The best way to protect yourself from COVID-19 is to get vaccinated

The CDC also recommends the following:

  • Regularly and thoroughly wash your hands with soap and water for at least 20 seconds or clean them with a 60% alcohol-based hand sanitizer. Avoid touching your eyes, nose, and mouth with unwashed hands.
  • Maintain at least six feet of distance between yourself and anyone who doesn’t live in your household. If someone in your home is sick, maintain six feet of distance from the sick person if possible.
  • Cover your mouth and nose with a mask when around others.
  • Cover your mouth and nose with your bent elbow or a tissue when you cough or sneeze, then dispose of the used tissue immediately.
  • Clean and disinfect frequently touched surfaces daily, including doorknobs, tables, light switches, countertops, handles, desks, phones, keyboards, toilets, faucets, and sinks.
  • Stay home if you feel unwell and, if possible, seek testing for COVID-19.


Does wearing a mask protect me from getting sick?

Wearing masks protects the wearer as well as others. Well-fitting masks filter out the majority of viral particles if worn properly.

SOURCE: Public Health On Call, CDC

Is hand sanitizer effective to protect against COVID-19?

If soap and water are not readily available, use a hand sanitizer that contains at least 60% alcohol. Cover all surfaces of your hands and rub them together until they feel dry.


Is there anything I can do to prepare just in case I or someone in my household gets COVID?

The best thing you can do is to follow prevention guidelines like wearing a mask, practicing social distancing, and avoiding close contact with others not in your household.

But there are other things you can do to be prepared in the event of illness such as knowing where and how to access testing, having a plan for quarantine and isolation, and understanding your employer's sick leave policy. Read more about how to prepare for COVID here

SOURCE: Johns Hopkins Bloomberg School of Public Health

What should I do if I am fully vaccinated and exposed to COVID?

The CDC is monitoring the COVID-19 pandemic and has issued interim guidance for exposure. This guidance is subject to change so please check the CDC's site for the latest


Is the public water supply safe from COVID-19?

There is no evidence of transmission through the public water supply.

SOURCE: Joshua Sharfstein

If multiple people in a household are positive, can they isolate together or do they have to be separated?

The goal of isolation is to avoid infecting people who are not already infected. Isolating separately is challenging, so if multiple people in a household have confirmed COVID-19, it’s fine for them to isolate together.

If one household member has COVID-19, that person should be isolated from others in the home.

SOURCE: Johns Hopkins Bloomberg School of Public Health

Does wearing two masks offer better protection than wearing just one?

If you do not have access to an N95 mask, one way to boost the protection of a cloth mask is by wearing a surgical mask underneath it. 

Important note: This guidance is not intended for a health care workers. That guidance can be found here.

SOURCE: Johns Hopkins Bloomberg School of Public Health

Are my pets at risk of getting sick?

Keep your pets—just keep your distance if you have COVID-19.

While few pet animals have been shown to carry SARS-CoV-2, and even fewer have gotten sick, it is possible for owners to transmit the COVID-19 virus to their pets. Cats and ferrets may be more likely than other kinds of pets to contract the virus. Some dogs have tested positive too.

The recommendation right now is to keep your distance from pets if you are diagnosed with COVID-19 or have been exposed to someone who tested positive. If you have COVID-19 and your pet is sick, please contact your veterinarian.

SOURCE: Meghan Davis

Can you get COVID-19 from second-hand smoke?

If someone is smoking a cigarette and coughing at the same time, maybe, but there’s not a biological mechanism for how the virus would be in the smoke.

SOURCE: Amesh Adalja

Does prone body position help very severely ill coronavirus patients in the intensive care unit?

There are reports that this can be helpful and there are more proning studies going on. The challenge with proning is that it is staffing intensive. You need a lot of staff to put people in the proning position and keep them that way—and a lot of PPE to do this safely.

SOURCE: Lauren Sauer

Wet markets in China are widely believed to be a source of new infections, including coronavirus. Should they be shut down?

Wet markets have come up in a number of contexts—certainly with COVID-19, and the 2003 SARS epidemic was linked to a wet market. The challenge with COVID-19 is that we don’t actually know much about the wet market that was involved. We know that the initial cluster of patients seen by clinicians had an occupational connection there. But we don’t fully know if and how they became infected at the wet market. It’s possible that the virus was circulating in the population and somebody who had it spread it at the wet market. We don’t know that it came from the animals there.

Wet markets have been identified as places of risk for the potential of animal viruses to spill over into human viruses, and there’s an active conversation around what to do about that. Some want to shut them down but worry it will just drive the practice underground in a way that authorities are unable to regulate. Others advocate for more regulatory approaches, so that when they occur, they occur as cleanly as possible.

SOURCE: Jennifer Nuzzo


Can people expect to be immune once they’ve had the virus?

If you’ve been infected, you have some protection but that immunity has limits. The biggest limit is that it doesn’t last long: immunity from natural infection starts to decline after a period of time.

Studies have shown that people who have been infected can benefit significantly from vaccination. It gives them a strong, lasting immunity boost.

SOURCE: Sabra Klein

Treatments and Vaccines

What treatments are there for coronaviruses?

There is no cure yet for COVID-19.

For individuals who do become sick, we have treatments that can be divided into different buckets. There's the antiviral treatments that prevent the virus from replicating or reproducing within the body. There are anti-inflammatory treatments which, if someone does develop severe disease from COVID, can shut down the inflammatory process and improve outcomes.

A game changer is the fact that we now have oral antiviral therapies that can be administered as pills: paxlovid and molnupiravir. If given to patients within 3-5 days of their symptom onset, it has been shown to reduce the risk of hospitalization.

Remdesivir is a widely used IV antiviral treatment that targets the RNA polymerase which is the way the virus can multiply and replicate itself. That drug has been shown for hospitalized patients to decrease the time it takes to get better and, in large retrospective studies, has been associated with an improvement in mortality. 

Monoclonal antibodies are an antiviral therapy. They're basically giving you a laboratory engineered antibody against the spike protein of SARS-CoV-2 so that your immune system can recognize it and clear it before you develop severe disease. They decrease the likelihood of hospitalization if you deliver these therapies before [the patient] gets sick. [But] different variants don't respond well to different monoclonals. Right now, we only have one in circulation for BA.2 but it's still effective at reducing hospitalization.

We also have convalescent plasma, which is taking the plasma of a person who was infected with COVID and made antibodies against SARS-CoV-2 and giving that to another patient who has not yet had a chance to make antibodies. If you deliver high-titer antibody plasma early on in someone's disease course, you can reduce the likelihood that they're going to get hospitalized. 

The New York Times Coronavirus Drug and Treatment Tracker is following treatments for effectiveness and safety. This resource is updated frequently.

SOURCE: Johns Hopkins Bloomberg School of Public Health and Public Health On Call

How does convalescent plasma work?

Convalescent serum is made from the antibodies made by people who have already recovered from COVID-19. It’s possible that giving these antibodies to people at high risk for exposure (like household contacts or health care workers), or to people early in infection, will be beneficial.

New research shows that early use of convalescent plasma may help outpatients avoid hospitalization if administered within 8 days of testing positive for SARS-CoV-2. 

SOURCE: Arturo Casadevall

Is there evidence for using hydroxychloroquine as a treatment for COVID-19?

Early questions about whether hydroxychloroquine might be of help to patients with COVID-19 have been addressed by high-quality research, and the results do not support the medication’s use. In June, the U.S. Food and Drug Administration found “no benefit for decreasing the likelihood of death or speeding recovery,” and revoked the medication’s authorization for use in COVID-19.

SOURCE: Joshua Sharfstein

Is it a good idea to get a flu shot?

It will be important to increase the proportion of the population vaccinated against flu as a means to protect ourselves and our communities, but also to save hospital capacity to treat those with COVID-19.

SOURCE: Public Health On Call podcast

What are mRNA vaccines and how are they different from other types of vaccines?

All vaccines deliver a viral protein that causes the person being vaccinated to make an immune response. There are different ways to do this: one is to give the whole, inactivated virus so that is doesn't make the person sick. 

Another way is to deliver the nucleic acid that encodes the protein and let the [vaccinated person's] cells actually make the protein. RNA is the nucleic acid that codes for proteins that cells make. It has all the information needed to be able to synthesize the protein. [mRNA vaccines] deliver the RNA that encodes the viral protein you're interested in and lets the cell actually make that protein to then stimulate the immune system. 

SOURCE: Public Health On Call Podcast

Are mRNA vaccines new?

Decades of research went into perfecting the mRNA technology platform. mRNA was first discovered in the 1930s and the first vaccines were tested in mice in the 1990s.

Although the first mRNA vaccines for humans were tested in 2013—and these were rabies vaccines—the technology had no commercial development opportunities until the COVID-19 pandemic which spurred manufacturers to develop dozens of vaccines against SARS-CoV-2 and brought tremendous increases in funding.

This is a technology that has been well studied and already, vaccine manufacturers are developing mRNA vaccines to protect against other diseases such as the flu and HIV. It's a new era for vaccine technology and production, and a testament to scientific progress and decades of research. 

SOURCE: Chris Beyrer

What makes mRNA vaccines so beneficial?

[mRNA vaccines] have several advantages. Because the cell itself is going to make the protein, it's much more likely to be the native protein or have the right properties that the virus would also have. 

Another big advantage is that they're fast to make. If you have the basic platform that [allow you] to insert the sequence for your particular protein of interest, you can just take [that] out and put another one in. It's very fast to substitute in a new, different coding sequence for a protein.

SOURCE: Public Health On Call Podcast

Will mRNA vaccines work against different variants of COVID-19? 

So far, mRNA vaccines appear to be quite effective against different variants of COVID-19. But this could change and if new mutations notably alter the protein’s structure, new variants could elude the antibodies elicited by vaccines for other variants.

Fortunately, mRNA vaccines are well-suited for keeping up with sudden changes like these. The mRNA itself is manufactured via a standardized process in which the core ingredient is a DNA sequence encoding a specific viral protein. This means vaccine makers can update the vaccine for new strains by tweaking the “recipe” to encode a new protein.

SOURCE: Gigi Gronvall

Why were we able to adapt the mRNA platform for the virus that causes COVID-19 but not flu or other viruses? 

The first mRNA vaccines using these fatty envelopes were developed against the deadly Ebola virus, but since that virus is only found in a limited number of African countries, it had no commercial development in the U.S.

This is a technology that has been well studied and already, vaccine manufacturers are developing mRNA vaccines to protect against other diseases such as the flu and HIV. It's a new era for vaccine technology and production, and a testament to scientific progress and decades of research. 

SOURCE: Chris Beyrer

Will we use the mRNA platform to make other kinds of vaccines?

Already, vaccine manufacturers are developing mRNA vaccines to protect against other diseases such as the flu and HIV. It's a new era for vaccine technology and production, and a testament to scientific progress and decades of research. 

SOURCE: Chris Beyrer

If a vaccine is showing "95% efficacy", does that mean that 5% of people who are vaccinated would still get COVID? 

There's a lot of different ways that people calculate efficacy. Think about it as if you were vaccinated and your friend was not vaccinated, and you were both exposed to the same amount of virus. Your risk of coming down with COVID is 95% reduced compared to your unvaccinated friend. 

Some other vaccines offer 50% efficacy. When you think of it in those terms—if you have a 50% reduced risk of coming down with disease [compared to] an unvaccinated person exposed to the same amount of virus—it's still a pretty good risk calculation for yourself. 

95% efficacy is amazing. That's more like the efficacy that we see for childhood vaccines—diphtheria, MMR, tetanus, or measles. 

SOURCE: Gigi Gronvall

How do we know that the vaccines are safe, given how quickly they were developed?

As of May 2021, more than 100 million Americans have been fully vaccinated. Public health agencies have been closely watching for any safety signals and we have safety data going back as far as August 2020 when Pfizer and Moderna first began vaccinating Phase 3 clinical trial participants.

In the United States, the FDA has required the same large clinical trial that it would otherwise require for a vaccine. We didn’t do what some other countries did and approve it just based on some blood test results; we actually looked at tens of thousands of people to see whether or not it prevented the disease.

One of the ways the process was sped up is that the taxpayers put a lot of money into this program—that was run out of the White House—to allow companies to basically start each part of the process right from the beginning.

Typically, what would happen is a company might do one study and see whether it works. If it doesn’t work, then they’re done. If it does work, then they start planning the next phase. And if that phase works, then they start planning the next. Everything is A, then B, then C. But with the money that the taxpayers put forward, the companies were able to do A, B, and C all at once. So, they started that first phase and if that worked, they were ready to get going on that second phase. If it wasn’t going to work, they would have lost all the money [spent] preparing for the second phase.

But what they gained was time. They were able to move from A, to B, to C so much quicker because they didn’t have that period in between where they were assessing and figuring out what kind of investment [would be needed] for the next round.

SOURCE: Joshua Sharfstein and Johns Hopkins Bloomberg School of Public Health

There is misinformation circulating that COVID-19 vaccines contain mercury, anti-freeze, animal blood, or even formaldehyde. What is behind these claims?

COVID vaccines are new, but these kinds of concerns about vaccines go back for a long time. These are often intentionally a misconstruction of information by people who are anti-vaccine. 

Do they include animal blood? Do they include formaldehyde? No, they don't. Some [vaccines] do have preservatives, but all of them have been tested many times and have a good safety record, particularly in the quantities that are in the vaccine. A lot of times, people forget that we ourselves are made up of chemicals, and some of these things in the vaccine, there are sometimes more of them in your own body naturally. 

It's important to be aware of your sources of information about the vaccine and also to recognize that there are groups that are intentionally poisoning the information atmosphere with things that are not true about the vaccine. Some don't really care about vaccines and are not really “anti-vaccine.” They're just really trying to sow discord.

A good hint of whether the information comes from a source that's intending to sow discord is if it makes you angry, if it inspires a powerful emotion. Just take the next step and look at your source. See if [the information] is coming from a place where there are people who are experts in that topic, who can address the concerns but without trying to manipulate you.

I've even heard [the claim] that there was some sort of chip in the vaccine—that is not possible and not something that is in these vaccines

SOURCE: Gigi Gronvall

Can protection from mRNA vaccines work against new variants of the virus?

So far, it looks like the mutations that are in the spike protein in these different variants are not going to let the virus escape the vaccine. This could change—particularly as SARS-CoV-2 continues to spread throughout the world, with each new host creating opportunities for mutation. If these mutations notably alter the protein’s structure, new variants could elude the antibodies elicited by vaccines for other variants.

Fortunately, mRNA vaccines are well-suited for keeping up with sudden changes in the viral landscape. The mRNA itself is manufactured via a standardized process in which the core ingredient is a DNA sequence encoding a specific viral protein. This means vaccine makers can update the vaccine to fend off new strains by simply tweaking the “recipe” to encode a new protein.

If this virus becomes endemic, it might be that new vaccine variants will need to be rolled out to match the variants that take root. 

SOURCE: Gigi Gronvall

What are randomized control trials?

A randomized control trial is a study design where a patient is randomized to either option one or option two, sometimes multiple options, and sometimes one of those options is a placebo. That study design allows us to control for factors that may influence our ability to see the benefits and the risks associated with something like a treatment.

It’s really important in this setting because we don’t know much about COVID-19. The design is how we identify medical countermeasures, vaccines, medications.

SOURCE: Lauren Sauer

Do the COVID-19 vaccinations impact fertility in men and women?

There is no basis for believing that they impact fertility. 

SOURCE: Joshua Sharfstein

Should pregnant women get vaccinated for COVID-19?

The CDC encourages all pregnant people or people who are thinking about becoming pregnant and those breastfeeding to get vaccinated to protect themselves from COVD-19.


Should I expect side effects from COVID-19 vaccines?

Side effects may vary with the type of COVID-19 vaccine. We know the most about side effects following vaccination with the Pfizer and Moderna messenger RNA—or mRNA—vaccines. 

The most common side effect is soreness at the site of injection. Other side effects include fatigue, headache, muscle aches, chills, joint pain, and possibly some fever.

SOURCE: William Moss

How long do side effects from COVID-19 vaccines last?

Usually 24 to 48 hours, and no more than a few days.

SOURCE: William Moss

Since COVID-19 vaccines come in two doses, will I experience the same side effects after each dose?

Side effects were more frequent after the second dose in the vaccine trials.

SOURCE: William Moss

Do side effects differ from one manufacturer's vaccine to another?

Side effects are similar after the Pfizer and Moderna mRNA vaccines but could differ with other types of vaccines.

SOURCE: William Moss

Can side effects be more pronounced in people who are at higher risk of severe COVID-19 disease, like those who are older or who have comorbidities?

No—in fact, vaccine side effects have been less frequent and severe in adults older than 55 years in the vaccine trials.

SOURCE: William Moss

How do I know if my side effects are normal or if I should alert my doctor or health care provider?

You will be told about the side effects of the vaccine and when you should consult a health care worker at the time you are vaccinated.

The Centers for Disease Control and Prevention advises that you should contact your doctor or health care provider if the redness or tenderness where you got the shot increases after 24 hours, or if your side effects are worrying you or do not seem to be going away after a few days.

SOURCE: William Moss

Is it possible to contract COVID-19 between vaccine doses? 

Yes—and this is why it is important to continue to wear a mask, practice social distancing, and wash your hands. 

The first dose will not provide complete protection, and it will take about seven days after your second dose before you will achieve a full protective level of immunity that develops in about 95% of vaccine recipients. If you are exposed to SARS-CoV-2 before this time, it is possible that you could develop COVID-19. 

Even once you have received both doses of the COVID-19 vaccine, it will still be important to continue practicing public health mitigation strategies like masks and distancing until the pandemic is under control and we know more about how the vaccines prevent transmission. 

SOURCE: William Moss

How will I know whether I am experiencing side effects or possible COVID-19 infection?

The side effects of the vaccine typically start within 12 to 24 hours of vaccination, but it may be difficult to tell the two apart if you become infected between vaccine doses.

If you experience side effects that last beyond 48 hours, you should contact your doctor or medical provider for advice. 

SOURCE: William Moss

Should people who already had COVID-19 and recovered still be vaccinated?

Yes! Prior infection with COVID-19 does offer some protection, but it’s limited: Immunity from natural infection starts to decline after 6-8 months.

Studies have shown that people who have been infected can benefit significantly from vaccination. After receiving the first dose of the Pfizer or Moderna vaccine, they have immunity levels comparable to those of uninfected people who have received their second dose.

SOURCE: Sabra Klein

If I've had COVID, how long should I wait to get vaccinated? Is it ok to get my first dose if I no longer have symptoms? 

If you are sick, stay home until you get better, which is around 10 days and no symptoms—then it’s fine to get vaccinated.

There are people who may get COVID right after their first shot, before there’s any protection, and they could get vaccinated for their second shot on time if they want, with one exception: If they’ve been treated for that COVID infection with antibody treatment, then there’s a recommendation to wait 90 days so that that antibody treatment doesn’t interfere with the vaccination.

SOURCE: Joshua Sharfstein

Since there’s a chance I could get sick from the vaccine’s side effects, is it better to get infected with COVID-19 naturally than to get vaccinated? 

No. Vaccines are tested for their safety in ways we could never do with a natural viral infection. A lot of what are referred to as side effects are the precise things we experience to a greater degree when we are infected: fever, headache, malaise, gastrointestinal issues, etc. With infection, you don’t know how bad it’s going to be. By not getting vaccinated, you’re rolling the dice. You may become severely ill. You may have to be hospitalized. You may die. There’s also the risk of long COVID.

SOURCE: Sabra Klein

If I am fully vaccinated and I catch another variant, will I acquire additional immunity?

It's likely that when you get a natural infection, you are going to be exposed to proteins of the virus that are not contained in the vaccine.

So, you likely will get a boost to your immunity, and maybe some different elements of your immunity will get stimulated with the natural infection. 

SOURCE: Amesh Adalja

If I get vaccinated, will I give my infant child an increased risk of getting sick from a COVID variant?

No. The best way to protect your infant (who's too young to be vaccinated) is for you to be vaccinated. That makes it much less likely that you will bring COVID-19—in any of its variant forms—into your household.

SOURCE: Amesh Adalja


Social Distancing and Other Public Health Measures

What are best practices for businesses to protect employees and customers?

The Center for Health Security has an Operational Toolkit for Businesses Considering Reopening or Expanding Operations in COVID-19. The toolkit includes an instruction manual, business risk worksheet, and an assessment calculator.

SOURCE: The Center for Health Security

Is temperature monitoring effective?

Taking temperatures is a very insensitive and imprecise tool. A fever is not always present with COVID-19 disease.

People can also have elevated temperatures for all sorts of reasons that don’t correlate with illness, such as exercise , or they can suppress their fevers by taking Tylenol or other over-the-counter medications.

SOURCE: Eric Toner

What are the best ways to do contact tracing?

A great resource on contact tracing is the Johns Hopkins COVID-19 contact tracing course, which is available for free on Coursera. (If you have taken the course, check out this resource of Frequently Asked Questions about contact tracing jobs and opportunities.)

In the U.S., the commitment to contact tracing programs, to getting them to the scale and speed that we need, has really varied by state and by jurisdiction. It’s clear across the U.S. right now that very few places that have the programs, the interventions in place, to keep transmission under control. Contact tracing has to be part of that. But there are other interventions to reduce the number of contacts that people have every day to go along with it.

Contact tracing can only work if you can find cases, and we are still not there with testing in the U.S.

SOURCE: Emily Gurley

Are there effective contact tracing apps or tech platforms?

Contact tracing is critical to managing transmission, but it’s resource intensive and requires a lot of data gathering. This can strain public health departments and areas that can’t recruit or train tracers.

Digital tools can facilitate quick and effective communication and give access to real-time information. Contact tracing tools and apps can follow up with patients, notify individuals of potential exposure, and refer them to testing facilities and care if they develop symptoms. There are also apps that collect user-generated data where users report symptoms or fill out surveys that can help officials map outbreaks.

But these tools may be costly, and there are questions of usability of the platforms. There are also privacy considerations, as some apps require the use of Bluetooth and location sharing.

SOURCE: Smisha Argawal


What should families with unvaccinated children consider?

The virus is still with us and the pandemic is not over, particularly for families with young children and household members who are immune compromised. Consider a few key questions:

  • Whom will you be interacting with?
  • What is the current proportion vaccinated and the current spread of COVID-19 in my community?
  • Where will the interaction take place?
  • Is the interaction necessary and what are the policies in place?

SOURCE: Keri Althoff and Elizabeth Stuart


How should we be thinking about schools?

The biggest factor determining risk in schools is what the virus is doing outside of them. In places where you have a very high test positivity, like well into the double digits, that suggests that the outbreak is very widespread and that testing isn't keeping up.

Regardless of whether schools open online, in person, or with a hybrid approach, there will be learning disruptions to consider. COVID-19 is exacerbating growing inequities around achievement, development, and graduation rates.

Schools can also expect a year of uncertainty and should think about plans for positive cases among students, faculty, and staff, or spikes in community transmission. Teachers and parents will need to help children manage distress caused by uncertainty, distance learning, and fear, and school leaders and educators will need to plan for different scenarios.

SOURCE: Johns Hopkins Bloomberg School of Public Health

How can schools develop a COVID-19 testing strategy?

Designing an effective testing strategy will require careful consideration of your group’s goals, resources, and structure. A testing strategy is a tailored plan that not only includes identifying the actual tests used but also describes the steps and factors to address to ensure that testing is rolled out in an effective way. In this section, we identify important factors you that can help you design your own testing strategy.

While a testing strategy will be unique to each organization, group, or individual, a few common factors should be considered when creating any testing plan:

  1. Are you trying to determine a current or past infection?
  2. Would you prefer to have samples collected at home or by a trained professional?
  3. How many people will be tested?
  4. What age groups will be tested?

SOURCE: The Center for Health Security's Testing Toolkit


How should we think about the need for racial and ethnic diversity in clinical trials for COVID-19 vaccines?

It’s critically important that we have racial and ethnic diversity.

We know that COVID causes increased rates of severe disease in Latinx and Black populations and in Native American populations. We will certainly want to be able to offer these COVID vaccines to these high-risk populations and encourage their use. But we need to know how well these vaccines work in these populations—if different vaccines work differently—so that we can offer the most effective vaccines.

SOURCE: Ruth Karron

Why are Black and other communities of Color being hit especially hard by COVID-19?

Before COVID-19, minority communities were already disproportionately impacted by health inequities. People in those communities already have higher rates of obesity, diabetes, heart disease, and lung disease, so these are the folks who were actually going to be at more risk of getting seriously ill with COVID-19. These health inequities result from the financial stresses of being poor and the social stresses of being from a marginalized group with a history of institutionalized, sanctioned mistreatment by law enforcement and other societal institutions.

There’s a confluence of all these different factors—not having access to food, not having access to good quality housing, being crowded in small houses where there are multiple generations and unable to engage in social distancing or stock up on groceries for several weeks at a time, having to use public transportation, to work in essential jobs, and having less access to health care. These are all manifestations of structural racism.

SOURCE: Lisa Cooper

What can be done right now to reduce the toll of COVID-19 on Black and minority communities?

The biggest thing that can be done to protect Black and minority communities is to ensure equitable access to vaccines. 

Keeping an eye on the data is also an important priority: knowing who is impacted and where they’re impacted.

Communication is also really important—making sure that the public understands why we might be seeing these patterns, and that it’s more about our society and the way our resources and opportunities are allocated than it is about individual behaviors. We need to do what we can to better understand the challenges of those communities, engage with trusted leaders, listen with respect, and show empathy and concern. We need to recognize the remarkable contributions of African American communities and follow our words up with real actions that bring about positive change.

We also need to focus on frontline workers and low-wage workers, and understand their needs—providing protective equipment, safe spaces to work, paid sick leave, hazard pay, or health insurance and access to testing and care. And, we need to provide for people’s basic needs: stable housing, food security, and digital access to education and health care.

SOURCE: Lisa Cooper



What are good sources of information?

Are there books for people to learn more about the public health response to similar situations?

The Public Health Crisis Survival Guide is for anyone involved in a public health operational role who may have to think about how to manage a crisis and maintain credibility in the face of uncertainty. D.A. Henderson’s Smallpox, the Death of a Disease has great information about operational challenges to confronting the spread of disease and the goal of trying to reduce its impacts on society.

SOURCE: Jennifer Nuzzo

How can I learn more from experts? 

The Johns Hopkins Bloomberg School of Public Health hosts a podcast called Public Health On Call, featuring interviews with experts and others on the front lines.

You can also stay informed and up-to-date about COVID-19 and other urgent public health issues by subscribing to the Expert Insights Newsletter, which publishes on Tuesdays and Fridays.