Evidence grows that vaccines lower the risk of getting long COVID

While many of the findings are still preliminary, the handful of studies that have emerged in the past half year are telling a relatively consistent story.

“It may not eradicate the symptoms of long COVID, but the protective effect seems to be very strong,” says epidemiology professor Michael Edelstein, of Bar-Ilan University in Israel, who’s studying long COVID.

Edelstein’s study was one of those included in a recent analysis of the evidence on long COVID and vaccination done by the UK Health Security Agency. That review found vaccinated people tend to have lower rates of long COVID after an infection than those who are unvaccinated.

There’s a running list of theories about why people get long COVID. Permanent tissue damage from the infection, injury to blood vessels and the development of microclots, a lingering viral reservoir in parts of the body, or an autoimmune condition are some of the ideas being explored in the research.

But even without a clear sense of what’s exactly driving long COVID, there’s good reason to believe that vaccines would help guard against the condition, says Dr. Steven Deeks, a professor of medicine at the University of California, San Francisco.

There’s overwhelming evidence that someone who’s vaccinated has less virus in their body during an infection, he says, “so it would make great sense that the amount of virus-related complications over time would also be lower.”

Looks good… but how good?

One of the ongoing challenges with long COVID research is simply defining the condition — with each study taking slightly different approaches as to what symptoms count and how long they need to last after the initial infection.

This inconsistency makes it hard to pull together a single estimate for how much vaccines limit long COVID.

Generally, though, Deeks says vaccinated people seem to have a 50% lower average risk of developing long COVID than unvaccinated people. This is in the range of what multiple studies in the U.K., Israel and the U.S. have found.

Ideally, long COVID should not be measured only a few months after the initial infection, he says. “A lot of people are still slowly getting better, so you have to wait at least four months to sort of figure out whether or not these symptoms will persist.”

The Israeli study, conducted by Edelstein and his colleagues, followed several thousand people who were unvaccinated, partially vaccinated and fully vaccinated. Those who tested positive were asked to self-report their symptoms between four and eight months after their initial infection.

Participants who had two or three doses of the vaccines were about 50% to 80% less likely to report seven of the 10 most common symptoms, which include shortness of breath, headache, weakness and muscle pain.

Edelstein says these results are not necessarily surprising, because they’re compatible with other recent studies. “It gives us a little bit of reassurance that if you’re vaccinated, you reduce your chances of long COVID quite substantially.”

Indeed, some researchers have found similar results by combing through electronic records from health care providers in the U.S. That massive study concluded that patients who had at least one vaccine dose were seven to 10 times less likely to report two or more long COVID symptoms compared to unvaccinated people between 12 and 20 weeks after their infection.

However, the evidence isn’t entirely conclusive. Some studies have not found as big a reduction. For example, the preliminary findings of a major study of electronic health records of U.S. veterans analyzed the medical problems affecting different organ systems at six months following coronavirus infection.

Being fully vaccinated did not appear to make a very meaningful difference for many of the post-infection complications, except in two particular areas, says the study’s author Dr. Ziyad Al-Aly, director of clinical epidemiology at the Veterans Affairs St. Louis Health Care System.

“People are having less lingering manifestations in the lungs and also less blood clotting,” he says.

The study also found that those who were hospitalized for COVID-19 had a higher risk of long COVID symptoms compared with those who had a mild illness, but that vaccines continued to make a big difference in reducing the risk of long COVID.

“The vaccines are supposed to protect you from being hospitalized,” says Al-Aly. “But even if they fail and you get breakthrough COVID and now you’re hospitalized, you still do better than someone who got COVID and was never vaccinated.”

Conflicting results in the studies may, in part, be due to how they’re conducted, such as differences in the methods of measuring long COVID, how symptoms are reported and the patient population being studied.

A good shield — but not perfect

Despite the promising evidence, long COVID researchers caution that vaccines can only do so much, and that invariably some people will still suffer symptoms even if they are vaccinated.

In fact, a recent study from the U.K. found that vaccines led to a significantly lower risk of long COVID compared with those who are unvaccinated, but that still close to 10% of the fully vaccinated participants showed symptoms of long COVID three months later.

David Putrino cares for long COVID patients who fit this very profile at the Mount Sinai Health System in New York City.

“I don’t think in good faith I would be able to distinguish between someone who has a breakthrough case of long COVID versus a pre-vaccine case of long COVID,” says Putrino, director of rehabilitation innovation at Mount Sinai. “The symptoms are very consistent.”

And there’s now another unresolved question facing researchers: How well do vaccines hold up against long COVID after an omicron infection?

Because omicron only emerged at the end of last year, there aren’t yet data on how many people have long COVID from the new variant, but Deeks says there are already some people who seem to be heading in that direction. “Without question, there are clearly people — I’m hoping not a lot — who got COVID a few months ago and are feeling ill today,” he says.

Based on what’s known about the variant, no one really knows for sure whether people who get omicron could be more, or less, prone to getting long COVID.

On the one hand, omicron is adept at evading the immune defenses put up by the vaccines, so it’s possible that “we might end up with more long COVID,” Deeks says.

Alternatively, the variant leads to a more localized infection and doesn’t spread throughout the body as much, which means there could actually be fewer instances of long COVID.

Deeks is leaning towards the more optimistic scenario. “That’s my prediction, but it’s just a prediction.”