Do vaccines protect against long Covid?

As the pandemic enters its third year, the long-term Covid becomes an increasingly important concern. And many people wonder if getting a Covid vaccine can reduce their chances of developing symptoms in the long term.

What does research show so far?

A growing number of studies suggest that getting a Covid vaccine can reduce – though not eliminate – the risk of lasting symptoms.

The UK Health Safety Agency (UKHSA) carried out an analysis of eight studies published on the topic before mid-January. She reported that six of the studies found that vaccinated people who were infected with the coronavirus were less likely than unvaccinated patients to develop symptoms of long-term Covid.

The remaining two studies found that vaccination did not appear to conclusively reduce the chances of developing long-term Covid.

How much protection can vaccines offer, according to studies that have found benefits?

Some study results suggest substantial protection, while others find only a small benefit.

A large study of electronic patient records at the US War Veterans Health Administration found that Covid-vaccinated patients had only a 13% lower risk than unvaccinated patients of showing symptoms six months later.

Two studies in Great Britain found a greater effect. A study of nearly 1.2 million people, based on patient reports via a mobile app, found a 50% lower risk of persistent symptoms among vaccinated patients. Another, which was not peer-reviewed and was based on a survey of nearly 6,000 patients, found a 41% lower risk.

A survey of US patients by healthcare data company Arcadia and the Covid Patient Recovery Alliance, a collaboration of experienced healthcare leaders in government and the private sector, found an even greater benefit.

The study, which has not been peer-reviewed, analyzed records of about 240,000 patients infected with the coronavirus through May 2021 and found that those who received a dose of the Covid vaccine before their infection were one-seventh to one-tenth of a second. probability of reporting two or more long-term Covid symptoms 12 to 20 weeks later.

That study also found that people who received the first dose of vaccine after contracting the coronavirus were less likely to develop long-term Covid than those who remained unvaccinated, and the earlier they were vaccinated after infection, the lower their risk of long-term symptoms. term.

A study in Israel, which was also not peer-reviewed, found through surveys that people immunized with two doses had between 54% and 82% lower risk than unvaccinated patients of reporting 7 of the 10 most common long-term symptoms. . They were generally no more likely to report symptoms such as headache, muscle aches and other problems than people in the general population who did not have Covid, the study said.

(The authors said they could not confirm whether patients were vaccinated before or after they contracted Covid, but that, due to Israeli vaccination policy, it was likely that most people who received two doses of the vaccine were infected with the coronavirus. some time after they received the injections.)

In the veterans study, also not yet published in a peer-reviewed publication, researchers compared about 48,000 patients who were not vaccinated when they had Covid with about 16,000 patients who were immunized.

Vaccinated patients were found to benefit primarily because they were less likely to develop lung problems and blood clotting difficulties, said one of the authors, Ziyad Al-Aly, head of research and development at the VA St. Louis and a clinical epidemiologist at Washington University in St. Louis. Other symptoms showed “very little risk reduction” from the vaccines, he said.

“The general message is that vaccines reduce, but do not eliminate, the risk of long-term Covid,” said Al-Aly, adding that “relying on vaccination as the only mitigation strategy is totally inappropriate. It’s like fighting with a shield that only works.” partially”.

What about studies that show no benefit?

In an analysis of electronic medical records of patients in the United States, researchers in Britain compared about 10,000 people vaccinated against Covid with a similar number of people who were not vaccinated against the coronavirus but against the flu – an attempt to limit the number of people in the study who could be considered undecided about vaccines or who generally have less healthy behaviors.

The study found that getting a coronavirus vaccine before being infected did not reduce the risk of most symptoms of long-term Covid. From the data, there was some suggestion that vaccinated people may be at lower risk for long-term symptoms such as abnormal breathing and cognitive problems, the authors wrote, but these results were not statistically conclusive.

The researchers said it is possible that because their data is based on electronic health records, the study only captured patients with the most severe symptoms, rather than a wider range of patients who did not seek medical care for their symptoms.

Why are the surveys conflicting?

One reason is the differences in the studies themselves. Not all researchers defined long-term Covid in the same way, measured the same symptoms, or tracked patients for the same length of time. For example, some studies recorded symptoms that remained at least 28 days after infection, while others measured symptoms that people had six months later.

Studies based on patient surveys can produce very different results than those based on electronic medical records. And some studies didn’t have very diverse populations. Patients in the veterans’ study, for example, were mostly older, white, and male.

Is there anything scientists can conclude for sure?

Yes. Vaccines are very effective in preventing people from becoming seriously ill due to infection with all variants known so far. And many studies have found that Covid patients sick enough to be hospitalized were more likely to have lasting health problems. So, by keeping people out of the hospital, vaccines should reduce the odds of this type of long-term post-Covid case.

Still, many people with long-term Covid had mild or even asymptomatic initial infections, and while some studies suggest that vaccines have the potential to alleviate their symptoms in the long term, the evidence is still not conclusive.

Vaccines offer some protection against infection to begin with — and avoiding infection, of course, is the surest way to prevent long-term Covid.

Can vaccination help if you already have long-term Covid?

When vaccines were first released, some patients with long-term Covid were finding that symptoms such as brain fog, joint pain, shortness of breath and fatigue improved after being vaccinated. Still, many people felt no difference in their symptoms after the immunization, and a small percentage said they felt worse.

A study by Britain’s Office for National Statistics found that in people aged 18 to 69 who reported their symptoms between February and September 2021, a first dose of a vaccine reduced the chances of reporting long-term Covid symptoms by 13% . A second dose further reduced the odds by 9%, the study found.

A recent review by the UKHSA evaluated that study and seven others that examined whether vaccinating people with long-term Covid affected their symptoms. It found that in most of these surveys, more people with Covid sequelae reported improvement in symptoms at some point after being vaccinated. However, other individuals also reported worsening of symptoms, and in several studies, most said that symptoms did not change.

The agency noted that the definition of long-term Covid varied widely between studies and that, as all studies were observational, changes in symptoms could be attributed to factors other than vaccination.

Translated by Luiz Roberto M. Gonçalves