Millions of people continue to suffer from long-term Covid symptoms. Studies estimate that 10 to 30 percent of people infected with the coronavirus may develop such symptoms, including cognitive issues, exhaustion, shortness of breath and many others.

“It involves a very varied constellation of symptoms, and it’s still quite mysterious,” said my colleague Pam Belluck, a health and science reporter. “But a growing number of studies are shedding light on the range of symptoms and what they look like. And we’re getting some scientific clues about what seems to be happening in the body.”

I spoke with Pam about our evolving understanding of the disease.

What causes long Covid?
There are different theories, but one of the leading theories has to do with the body’s inflammatory reaction.

When a virus enters the body, the immune system kicks into gear, it tries to fight the invader, and there’s a surge of inflammation. And according to this theory, too much inflammation can cause a range of damage, including to blood vessels and parts of cells that can then limit the body’s ability to use oxygen efficiently.
Another theory is that the body’s immune response didn’t shut down after the acute threat from the virus was defeated. It’s possible, scientists say, that there may be viral fragments that are hanging around at a very low level. They’re giving the immune system the instructions to stay on guard when there’s no reason it should be, and that over-activated immune response is causing symptoms.

Do we know who is more likely to get long Covid?
Recent research that followed a group of patients over time found that the people who were most likely to have long Covid two or three months after their infection had one or more of four biological factors.

One factor was that they had a high viral load in their blood from early in the infection. Another has to do with something called autoantibodies, which are usually associated with diseases like lupus or rheumatoid arthritis. Basically, they are antibodies that mistakenly attack body tissues, and if certain autoantibodies were present at the time of a Covid infection, those patients were more likely to develop long Covid.

The third one has to do with a virus called Epstein-Barr virus. It’s very common and it’s the virus that’s often associated with mono. Many people get infected with Epstein-Barr virus early in life and it might cause no symptoms, and it then becomes dormant. But patients in this study who ended up having reactivated Epstein-Barr virus at the time of their Covid infection were more likely to develop long Covid. Other clues suggest that some pre-existing conditions, like diabetes, may also predispose people.

If you’re vaccinated and you get Covid, are you less likely to have long-term symptoms?
Basically, we don’t know. A couple of studies have suggested that if you’ve been vaccinated and are then infected with Covid, it might make you less likely to have lingering symptoms, but at least one study suggested that vaccination didn’t make any difference.

One thing scientists are saying is that, so far, many long Covid studies have suggested that people who became really sick and were hospitalized from their initial Covid infection are more likely to have serious long-term symptoms. So if you consider that vaccines generally put you at lower risk for acute outcomes like hospitalization, then it makes sense that there might be some positive effect on reducing long-term symptoms. But having a mild Covid infection definitely doesn’t prevent long Covid — many people with long Covid did not get very sick initially or might even have had an asymptomatic Covid infection.

What’s your advice for people with long Covid?

Don’t be afraid to ask for help. There has been some skepticism about long Covid, including from primary physicians, and a lot of throwing up of hands. People may find that they go to their primary physician, and they get a scan, and nothing shows up. A lot of times there isn’t anything physically that an X-ray or blood test can show. But try not to be daunted. It may be better to try to seek help from a long Covid clinic at that point where at least you will get recognition that what you’re going through is a real thing and needs attention.

There are also a bunch of support groups and patient-led research groups that can be very helpful for tips of where to go, or at least just for sharing experiences. And know you’re not alone. There are a lot of people going through this.