As the pandemic enters its third year, Covid has long emerged as an increasingly important concern. And many people are wondering if getting a Covid shot can reduce their chances of developing long-term symptoms.
What does the research show so far?
The jury is still out, but a growing number of studies suggest that getting a Covid vaccine may reduce – but not eliminate – the risk of prolonged symptoms.
The UK Health Security Agency conducted an analysis of eight studies that had been published on the subject before mid-January. It reported that six of the studies showed that vaccinated people infected with coronavirus were less likely than unvaccinated patients to develop symptoms of long-term Covid. The remaining two studies showed that vaccination does not appear to definitively reduce the chances of developing long-term Covid.
How much protection could vaccines offer, according to studies that found benefit?
Some survey results suggest significant protection, while others find only a small benefit.
A large study of electronic records of patients in the U.S. Veterans Health Administration showed that vaccinated Covid patients had only a 13 percent lower risk than unvaccinated patients of developing symptoms six months later.
Two studies in the UK found a greater effect. A study of about 1.2 million people, based on patient reports via a phone app, found a 50 percent lower risk of persistent symptoms among vaccinated patients. Another, which has not been peer-reviewed and was based on studies of about 6,000 patients, found a 41 percent lower risk.
A study of U.S. patients conducted by Arcadia, a health data company, and the Covid Patient Recovery Alliance, a collaboration between leaders with health expertise 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 The study, which has not been peer-reviewed, analyzed records of about 240,000 coronavirus-infected patients in May 2021 and found that those who had received just one dose of a Covid vaccine before their infection were one-seventh to one-tenth of the probability of reporting two or more symptoms of prolonged Covid 12 to 20 weeks later. This study also showed that individuals who received their first dose of vaccine after receiving coronavirus were less likely to develop long-term Covid than those who remained unvaccinated, and the sooner they were vaccinated after infection, the lower the risk of long-term symptoms.
A study in Israel, which has also not been peer-reviewed, found through studies that people who received two doses of vaccine had between 54 percent and 82 percent lower risk than unvaccinated patients of reporting having seven of the 10 most common long-term symptoms. They were generally no more likely to report symptoms such as headaches, muscle aches and other problems than people in the general population who had never received Covid, the study said. The authors said they could not confirm whether patients had been vaccinated before or after receiving Covid, but said that due to Israeli vaccination policies, it was likely that most people who received two doses of vaccine were infected with coronavirus. once after they had become their shot.)
In the veteran study, which is also not yet published in a peer-reviewed publication, researchers compared about 48,000 patients who were unvaccinated when they received Covid with about 16,000 patients who were vaccinated. It found that vaccinated patients mostly benefited from being less likely to develop lung problems and blood clotting problems, said one of the authors, Dr. Ziyad Al-Aly, Head of Research and Development at VA St. Louis Health Care System and a clinical epidemiologist at Washington University in St. Louis. Louis. Other symptoms showed “very little risk reduction” from vaccines, he said.
“The overall message is that vaccines reduce but do not eliminate the risk of long-term Covid,” said Dr. Al-Aly, adding that “confidence in vaccination as the only mitigation strategy is completely inadequate. It’s like going into battle with a shield that only partially works.”
What about studies that show no benefit?
In an analysis of electronic medical records from patients in the United States, researchers in the UK compared around 10,000 people who had received Covid vaccines with a similar number of people who had not been vaccinated against coronavirus but who had received a flu vaccine – an effort to limit the number of people in the study who can be considered vaccinated or who generally had less healthy behavior.
The study showed that having a coronavirus vaccine before they were infected did not reduce the risk of most symptoms of long-term Covid. There were some suggestions from the data that vaccinated people might have a lower risk of long-term symptoms such as abnormal breathing and cognitive problems, the authors wrote, but these results were not statistically significant.
The researchers said it was possible that because their data relied on electronic health records, the study could have captured only patients with the most severe symptoms, rather than a wider range of patients who did not seek medical attention for their symptoms.
Why is the research contradictory?
One reason is the differences in the studies themselves. Not all researchers have defined long 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 lasted at least 28 days after infection, while others measured symptoms that people experienced six months later. Studies based on patient studies can give very different results than those based on electronic records. And some studies did not have very different population groups. Patients in the veteran study, for example, were mostly elderly, white, and male.
Are the results different for different variants of coronavirus?
Many of the published data followed patients infected early in the pandemic. Some recently published data included people infected with the highly contagious Delta variant, but it is too early for studies on vaccines and long Covid that includes the Omicron variant. It is also too early for studies evaluating the effect of boosters on long-term Covid.
Is there anything the researchers can conclude with certainty?
Yes. Vaccines are very effective in preventing people from becoming seriously ill from infection of all the hitherto known variants. And many studies have found that Covid patients who were 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 chances of that type of long-term post-covid case.
Yet many people with long-term Covid had mild or even asymptomatic initial infections, and although some studies suggest that vaccines have the potential to relieve their long-term symptoms, the evidence is not yet conclusive.
Vaccines provide some protection against getting infected to begin with – and avoiding infection is, of course, the safest way to prevent long-term Covid.
Does the vaccine label make a difference in potential protection against long-term Covid?
So far, studies have not found that different vaccines have different effects on long-term symptoms.
What are the possible scientific reasons why vaccines can protect against long-term Covid?
The cause of long-term Covid is still unclear, and different symptoms may have different underlying causes in different patients, scientists say. Some believe that the condition may be related to remnants of the virus or its genetic material that dwells after the first infection has disappeared. Another theory is that the persistent problems are related to inflammation or blood circulation problems spurred by an overactive immune response that is unable to shut down.
Akiko Iwasaki, an immunologist at Yale, has said that vaccines may be able to provide lasting relief in humans whose symptoms are caused by remnants of the virus, if the antibodies generated by the vaccines eliminate those remnants.
But in people whose symptoms may be caused by a post-viral reaction similar to an autoimmune disease, she said, vaccines can only help temporarily, and problems like fatigue can reappear.
Can it help to get vaccinated if you already have a long Covid?
When vaccines were first rolled out, some patients with long-term Covid found that symptoms such as brain fog, joint pain, shortness of breath, and fatigue improved after being vaccinated. Still, many people experienced no difference in their symptoms after vaccination, and a small percentage said they felt worse.
A study by the Office for National Statistics in the United Kingdom showed that in people aged 18 to 69 who reported their symptoms between February and September 2021, a first dose of a vaccine lowered the odds of reporting long-term Covid symptoms by 13 percent . Another dose lowered the odds further by 9 percent, the study found.
The recent analysis from the UK Health Safety Agency evaluated this study and seven others that investigated whether vaccination of people with long-term Covid affected their symptoms. It found that in most of these studies, several people with prolonged Covid reported improvement in their symptoms at some point after they had been vaccinated. However, some people also reported worsening of symptoms, and in several studies, the majority of people said that their symptoms were unchanged.
The Agency noted that the definition of long Covid varied widely among the studies and that, because all studies were observational, changes in symptoms could be due to factors other than vaccination.