Skip to main content

What We Do and Don’t Know About Long COVID and Long-Haulers

Up to a year after having COVID-19, some people have yet to fully recover.


Global reports show that a third of people who had COVID-19 experience lingering symptoms or new chronic health problems—some as long as a year after their initial infection.

There’s still much to be learned about this population, informally called “long-haulers,” including specific risk factors for and possible causes of this condition. Epidemiologist Priya Duggal, PhD ’03, MPH ’98, is studying Post-Acute Sequelae of COVID-19, commonly known as long COVID, through the Johns Hopkins COVID Long Study. In this Q&A, Duggal discusses what we know—and still need to learn about this health condition.

What exactly is long COVID? What are the symptoms?

With many infectious diseases, you have an acute phase, which is the initial phase where individuals may recover or resolve their infection, or they may go on to severe infections and potentially death. There’s also what we call the chronic state of infection, and that's what we're starting to see emerge in very large numbers for COVID. These are individuals who have post-acute sequelae (or symptoms) 30 days or more after their initial infection.

The symptoms we’re seeing with long COVID include things like loss of taste or smell, but also brain fog or an inability to concentrate. We also have individuals with new heart conditions, new kidney conditions, and, most prevalent, individuals who have excessive fatigue and difficulty breathing.

What do we know about those who experience symptoms associated with long COVID and the risk for developing it?

We’re seeing long COVID across the age spectrum. What’s really interesting and devastating is that we're seeing it develop among people who were mildly infected, moderately infected, and in some reported cases, those who were previously asymptomatic, as well as those who were hospitalized.

Some studies indicate that long COVID is a bit more prevalent in younger individuals—people in their 30s, 40s, and 50s. We see that younger women versus younger men seem to be reporting more long-haul symptoms, though it’s unclear if this is a reporting issue or if there’s actually a difference between the two.

At this point, we don’t know if there’s a higher risk for developing symptoms based on race or comorbidities. Until we get a handle on who’s at risk for long COVID, it’s going to be difficult for us to understand who we should be treating.

How prevalent is long COVID?

Global reports indicate about 20-30% of individuals who were infected with COVID-19 are reporting symptoms more than 30 days post-infection. These include several reports of symptoms three to six months post-infection and reports of long-term symptoms one year after infection.

What do we know right now about the effectiveness of vaccines in preventing long COVID?

It’s a little too early to tell. What we do know is that individuals who are vaccinated are less likely to get an infection (or reinfection). However, there are some COVID infections occurring post-vaccine. Although the number isn’t reportedly large, we are hearing that those individuals who have these “breakthrough infections” can experience the traditional symptoms of COVID. Given that they can have those symptoms, however mild they may be, it’s likely that they can also go on to long COVID. However, since we don’t know how or why long COVID affects certain individuals, it’s difficult to predict.

At this time we believe [that] if you can have those symptoms post-vaccine, then you could potentially go on to have long-term symptoms.

Can vaccines alleviate symptoms of long COVID?

There were some anecdotal reports of people with long COVID who were vaccinated and [then] their symptoms resolved (and others who were vaccinated and nothing changed). Some scientific groups are working on this question by checking the blood of those with long COVID pre- and post-vaccine. If the vaccine does resolve symptoms for some people, it may help us to understand why some people have long-term symptoms and maybe their bodies need that immune system boost that the vaccine provides. But it’s all speculation at this time. We are trying to quantify how many people may have symptoms resolved after vaccination in our survey to see if this is common or perhaps just some rare reports.

Are we seeing reports of long COVID in children and adolescents?

There are symptoms of long COVID in children and adolescents. Their symptoms are different from what we're seeing in adults, but just like with other infections, children can get an acute phase and they can get a chronic phase. The reported primary symptoms seem to be excess fatigue and an inability for them to do some of their daily tasks.

Are the features of long COVID different from symptoms of other post-viral syndromes or chronic fatigue syndrome?

I don’t think it necessarily represents what we see in chronic fatigue syndrome, but there are some similarities. What perhaps is unique about long COVID and is especially apparent is that many different organ systems are affected. For example, some people are reporting specific heart issues, and others are reporting difficulty breathing, or dyspnea, and that has a lot to do with the lungs specifically being affected. But there isn't one classic set of symptoms that all of the long-haulers are expressing. We hope that what we learn from long COVID aids the chronic fatigue community, which has faced numerous struggles with the clinical community to even get recognition of their symptoms. We can learn from this, and we can hopefully provide the necessary estimates on the number of those affected and start to define this disease, as well as conduct rigorous research to evaluate potential risk factors and mediating factors.

Long-haulers have real symptoms, and it is imperative that our focus be twofold—on the acute phase of the infection that may result in hospitalization and death, and also on those who have persistent or chronic long-term symptoms.

Carly Kempler is the media and audience engagement specialist for the Johns Hopkins Bloomberg School of Public Health.