As long Covid becomes the 'pandemic after the pandemic,' many people wonder whether being vaccinated reduces the risk of long-term symptoms, Pam Belluck writes for the New York Times. 

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How could vaccines protect against long Covid?

So far, the cause of long Covid is unknown, particularly since it can manifest as different symptoms in different patients. Some scientists posit that the condition may be caused by lingering genetic material from the coronavirus, while others believe that symptoms may be due to inflammation or circulatory problems.

According to Akiko Iwasaki, an immunologist at Yale University, if a person's symptoms are caused by remnants of the coronavirus, antibodies generated from Covid-19 vaccines could potentially destroy these remnants and get rid of lingering symptoms.

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However, Covid-19 vaccines may be less effective for people whose long Covid symptoms resemble an autoimmune disease, Iwasaki said. In this case, the vaccine could temporarily relieve symptoms, such as fatigue, but they would eventually re-emerge.

Currently, there is not conclusive evidence on how vaccines affect long Covid, but a growing number of studies suggest that being vaccinated may reduce—although probably not eliminate—the risk of long-term symptoms, Belluck writes.

What current research suggest

In an analysis of eight studies on vaccines and long Covid, the U.K. Health Security Agency found that six studies suggested that people who were vaccinated were less likely to develop long Covid symptoms than unvaccinated patients after being infected by the coronavirus. The remaining two studies could not conclusively say vaccines reduced the chance of developing long Covid.

Similarly, other studies have found that Covid-19 vaccines may be protective against long-term symptoms, but the level of protection found varied.

For example, a preprint study from Israel found that patients who had received two doses of a Covid-19 vaccine were between 54% and 82% less likely to report having seven of the 10 most common long Covid symptoms, including headache and muscle pain, compared to unvaccinated patients.

In addition, another preprint study from Arcadia and the Covid Patient Recovery Alliance analyzed EHRs from roughly 240,000 patients who had been infected by the coronavirus by May 2021 and found that even one dose of a vaccine reduced the risk of reporting two or more long Covid symptoms 12 to 20 weeks later compared with unvaccinated patients.

Two studies in Britain also found similar, if smaller effects. In one study, researchers analyzed online reports from around 1.2 million people and found that vaccinated patients had a 50% lower risk of long-term Covid-19 symptoms. Another study, which has not yet been peer-reviewed, surveyed around 6,000 people and found a 41% lower risk of long Covid among those who were vaccinated.

However, other studies have found limited to no effects of vaccination on long Covid.

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For example, a preprint study of roughly 60,000 patients in the U.S. Veterans Health Administration found that vaccinated Covid-19 patients only had a 13% lower risk of long Covid symptoms six months later than unvaccinated patients. According to Ziyad Al-Aly, chief of research and development at the V.A. St. Louis Health Care System and a clinical epidemiologist at Washington University in St. Louis, vaccinated patients were less likely to experience lung and blood clotting problems, but other symptoms had "very little risk reduction" from vaccines.

Separately, a study comparing patients who had received Covid-19 vaccines to those who had not but had received a flu vaccine found that being vaccinated against Covid-19 did not reduce the risk of most long Covid symptoms. Although the data suggested that vaccinated people may be at lower risk of long-term symptoms such as abnormal breath and cognitive issues, the evidence was not statistically conclusive.

According to Belluck, these varied study findings may be due to differences in how the studies were performed or their patient populations. "Not all researchers have defined long Covid in the same way, measured the same symptoms or tracked patients for the same length of time," she writes. Some studies only tracked patients for 28 days, while others followed them for six months. In addition, studies that used patient surveys may result in different findings than those that used EHRs.

Based on these studies, "[t]he overall message is that vaccines reduce but do not eliminate the risk of long Covid," Al-Aly said. "[R]eliance on vaccination as a sole mitigation strategy is wholly inadequate. It is like going to battle with a shield that only partially works."

Can vaccines help if you already have long Covid?

According to Belluck, after Covid-19 vaccines first became available, some patients with long Covid reported that their symptoms, including joint pain, brain fog, shortness of breath, and fatigue, improved after being vaccinated. However, many other long Covid patients reported no differences after vaccinated, and a small proportion even said their symptoms worsened.

So far, research suggests vaccination has a limited impact on patients who already have long Covid. In a study from the U.K.'s Office for National Statistics, researchers found one vaccine dose reduced the risk of reporting long Covid symptoms by 13% among patients ages 18 to 69 who reported symptoms from February to September 2021. A second vaccine dose then further reduced this risk by 9%.

Overall, while vaccines may not be able to completely prevent long Covid, they are very effective at preventing serious illness and hospitalization. According to Belluck, "by keeping people out of the hospital, vaccines should reduce the chances of" significant, long-term health issues.

In addition, vaccines do provide some protection against coronavirus infection, "and avoiding infection, of course, is the surest way to prevent long Covid," Belluck writes. (Belluck, New York Times, 4/26)