Study shows vaccines reduce risk of long-term Covid-19 illness

A large new study provides some of the most compelling evidence to date that Vaccines reduce the risk of developing persistent or long-lasting COVID.

Scientists analyzed infected people in the United States during the first two years of the pandemic and found that the percentage of vaccinated people who developed persistent Covid was much lower than the percentage of unvaccinated people who were vaccinated.

Medical experts have previously said vaccines could reduce the risk of long-term Covid illness, in large part because they help prevent serious illness during infection, and people with severe infections are more likely to experience long-term symptoms.

But many people with mild infections also develop persistent Covid, and a study published Wednesday in the New England Journal of Medicine found that vaccination did not eliminate all risk of developing the diseasewhich continues to affect millions of people in the United States.

“There was a residual risk of persistent Covid infection among vaccinated people,” he wrote in an accompanying editorial. Clifford Rosena senior scientist at the MaineHealth Research Institute who was not involved in the study. For that reason, Rosen added, new cases of persistent Covid “may continue without decreasing.”

The study assessed the medical records of millions of patients in the Department of Veterans Affairs health care system. It included nearly 450,000 people who had Covid between March 1, 2020, and January 31, 2022, and about 4.7 million people who were not infected during that time.

The veterans studied were significantly less diverse than the general U.S. population. Nearly three-quarters of the participants were white, about 91 percent were men, and their average age was 64.

The researchers analyzed medical records to calculate the percentage of Covid patients who still had Covid a year after infection. The lowest rate of persistent Covid infection in the study, 3.5 percent, was seen among vaccinated people who became infected during the final study period, from mid-December 2021 to January 2022.

By comparison, among unvaccinated patients in the study who became infected during the same period, the rate was 7.8 percent.

“We found that most of the decline was due to vaccination.”said the study’s lead author, Ziyad Al-AliDirector of Research and Development at the St. Louis Veterans Affairs Health Care System and a clinical epidemiologist at Washington University in St. Louis.

However, he said, “the effectiveness of the vaccine declines significantly over time and people are not aware of the annual vaccinations.”

He added: “We can’t have it all. We can’t say that the long-term incidence of Covid has been reduced by vaccines and then refuse to vaccinate. That will lead to cases increasing again.”

To rule out other possible causes, the researchers looked at comparisons between uninfected people who developed similar symptoms, Al-Ali said.

For example, the main symptoms of long-term covid, such as tiredness and brain fogcan also affect patients with cancer and other diseases, so the authors subtracted the incidence of these symptoms in the uninfected population from the number of infected people to calculate the percentage attributable to persistent Covid, he said.

The study covered the period between the initial emergence of the coronavirus and the emergence of two more contagious variants, delta and omicron, after vaccines were introduced. The authors compared outcomes between vaccinated and unvaccinated patients, but did not calculate the incidence rate for both groups together.

The researchers found that among unvaccinated people infected between June 19 and December 18, 2021, when the delta variant was dominant, the rate of persistent Covid a year later dropped slightly to 9.5 percent from 10.4 percent among those infected in the first 15 months of the pandemic.

That rate dropped further, to 7.8 percent, among unvaccinated people infected between December 19, 2021, and January 31, 2022, during the omicron surge.

Among vaccinated people who were infected, the rate of persistent Covid infection was markedly lower. The authors said that differences in variants and other aspects of the delta and omicron variant periods played a role, but they attributed about 72 percent of the decline to vaccines.

About 5.3 percent of those infected during the delta variant developed persistent COVID-19 a year later, while 3.5 percent of those infected during the omicron variant had it.

“This is lower than in previous stages, but not low,” Al-Ali said. “Multiply that by the huge number of people who continue to become infected and re-infected, and 3.5 percent per 100 infected adults translates into millions of additional cases of long Covid.”

The researchers didn’t look at more recent time periods, but a recent study from the Centers for Disease Control and Prevention found that about 5.3 percent of U.S. adults — about 13.7 million people — currently have persistent Covid.

The authors noted that long-term Covid symptoms in most categories, including cardiovascular and kidney problems, decreased during the first two years of the pandemic, but Gastrointestinal, metabolic, and musculoskeletal problems increased in the omicron variant era in unvaccinated individuals.likely reflects changes in the virus and other factors.

Pam Bellack is a health and science reporter covering a wide range of topics, including reproductive health, long Covid, brain science, neurological disorders, mental health and genetics.

© The New York Times, 2024