Daniel Griffin wasn’t sure what to expect when his patients with chronic COVID-19 symptoms started getting vaccinated. There was some concern that the shots might make things worse by triggering the immune system. Luckily, the opposite seemed to be true.

“I started getting texts and calls from some of my colleagues saying hey, are your patients with long COVID reporting that they’re feeling better after the vaccine?” says Griffin, an infectious diseases clinician and researcher at Columbia University. When he started talking with patients, he saw that they were. “It’s not 100 percent, but it does seem like to be around a third,” he says.

Early reports from Griffin and others hint that people with persistent symptoms may improve after getting vaccinated. Information is still limited, and the data is largely anecdotal — but if the pattern holds, it could help researchers understand more about why symptoms of COVID-19 persist in some people, and offer a path to relief.

Many of Griffin’s patients who improved had significant side effects after their first shot of either the Moderna or Pfizer / BioNTech vaccine. That’s common in people who’ve had COVID-19 before — they already have some level of antibodies, so the first shot acts more like a second booster. Then, his patients with chronic symptoms started to report that their sense of smell was improving or that they weren’t as fatigued. “For some of them it was short lived. But for a chunk, it actually persisted — they went ahead, got their second shot out, and are saying, wow, they really feel like there’s light at the end of the tunnel,” Griffin says.

A number of people who catch COVID-19 experience symptoms — like fatigue, shortness of breath, or loss of smell — months after their initial illness. For some, those symptoms are debilitating. Many people who got sick during the first wave of the pandemic a year ago still aren’t fully recovered. Doctors like Griffin are learning more about what’s being called “long COVID,” but answers are still limited. Any hint of a path toward relief “would be nothing short of a miracle,” says Diana Berrent, founder of the COVID-19 survivors and long-haulers group Survivor Corps.

Some patient surveys are trying to get an early read on how widespread improvement is. Director Gez Medinger, who covers long COVID on his YouTube channel, surveyed nearly 500 people in various long-hauler support groups on Facebook. Around a third of people surveyed said that they felt slightly or entirely better when they were at least two weeks out from vaccination.

Dozens of people who responded to a poll in the Facebook group for Survivor Corps said that their symptoms improved slightly or went away almost completely. “We were really concerned that people were going to have bad reaction. It never occurred to us that they would actually improve,” Berrent says. Another survivors group, Patient-Led Research, is also surveying people with long COVID who have been vaccinated.

There are limitations to these types of surveys — they’re small, and they’re limited to people who seek out and participate in support groups. They can’t prove that the vaccine was what led to any symptom improvement. But they can point researchers toward useful research questions.

There are plausible biological reasons vaccination could help people with long COVID, says Akiko Iwasaki, an immunologist at Yale University. Scientists still don’t know for sure why some people have chronic symptoms, but one theory is that the virus or fragments of the virus stick around in their body. They’re not contagious, but the leftovers continue to irritate the immune system. Vaccination could clear those out. “Potentially, those remnants are removed because you’re generating a lot of antibodies,” Iwasaki told The Verge.

Another theory is that, for some people, COVID-19 triggers long-lasting changes in the immune system, and it could turn on healthy cells and tissues. In that case, the vaccine might help by giving a jolt to the immune system. “It can reset some of those existing responses,” Iwasaki says. In that case, symptom improvement would probably be short-lived and only last as long as the vaccine’s kick does.

There’s a lot more to learn about the relationship between long COVID and vaccines. It’ll take more and more rigorous, survey data to understand exactly what portion of people feel better after they get vaccinated. There are studies underway that monitor certain inflammatory proteins in the blood of people with chronic symptoms, and researchers could compare levels in people who are and aren’t vaccinated, Griffin says.

Research should also check if one type of vaccine is more effective at reducing chronic symptoms than the others. Even though Moderna, Pfizer / BioNTech, and Johnson & Johnson vaccines work equally well at preventing severe infection, they might vary in how well they could help people with long COVID. “Once we know that, we can recommend among COVID people to get different vaccines,” Iwasaki says.

That data would also help clarify the reasons people have chronic symptoms. If a significant number of people have long-term improvement after they get vaccinated, Iwasaki says she’d lean toward the viral remnants theory. “For that, once you get rid of the virus, that’s it — you don’t suffer from this anymore.” She notes, though, that everyone has different experiences with the disease. “It’s not a one size fits all.”

Berrent still thinks it’s too early to say for sure how much vaccines can actually help people with long COVID. “I think this is all very interesting,” she says. “I feel like we’re still gathering data here.” It is encouraging, though, to see that they aren’t having bad reactions to the vaccine, and any minor improvement is exciting.

The early reports are a good push for people with chronic COVID-19 symptoms to get vaccinated, Griffin says. “It doesn’t look harmful, and it may be therapeutic. I think it’s encouraging for people with long COVID to get signed up as soon as they can.”