When researchers began studying Long COVID, after it became clear in 2020 that some people don’t recover from COVID-19 right away, some estimated that roughly a third of people who caught the virus experienced long-term symptoms.
But that was years ago, at a time before vaccines and endless iterations of Omicron, when most people had been infected once, if ever. How has the risk of contracting Long COVID changed over the years, as the virus has evolved and almost everyone in the U.S. has gotten vaccinated, infected, or both (sometimes many times over)?
Recent research offers promising signs that Long COVID is becoming less of a threat with time. But, experts say, there’s still reason for caution.
One study, published July 17 in the New England Journal of Medicine, tracked a steady decline in the incidence of Long COVID from 2020 to 2022. Among people in the study who got COVID-19 during the Delta era, 5.3% of those who were vaccinated and 9.5% of those who were unvaccinated had Long COVID symptoms a year later. Among people who got sick during the Omicron era, those numbers dropped to 3.5% and 7.8%.
Those findings, based on health records from almost 450,000 Department of Veterans Affairs patients who caught COVID-19, are “good news,” says study co-author Ziyad Al-Aly, a clinical epidemiologist at the Washington University School of Medicine in St. Louis. “The risk of Long COVID after SARS-CoV-2 infection declined over the course of the pandemic.”
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It’s impossible to tell from the study whether risk has continued to decline with each Omicron subvariant that has emerged since 2022, but Al-Aly says his hunch is that it has. About 5% of U.S. adults say they currently have Long COVID, as of the latest Census Bureau estimate, down from more than 7% in the summer of 2022.
Vaccination, which previous research shows can protect against Long COVID, seems to be a major explanation for Long COVID’s decline—a good reason to keep current with shots as new ones come out, Al-Aly says. But the virus’ evolution and advancements in medical treatment, such as use of the antiviral Paxlovid, may have also contributed, he says.
Another recent study, published July 11 in Communications Medicine, suggests another possible factor. Reinfections—which account for an increasingly large share of COVID-19 cases, now that most people have already had the illness—may be less likely to result in Long COVID than primary infections. (Al-Aly’s team did not assess the effect of reinfection in their paper.)
After analyzing health records from about 3 million people included in RECOVER, the National Institutes of Health’s (NIH) Long COVID research project, the researchers found that, in each era of the pandemic, Long COVID was diagnosed more frequently after first rather than second infections. “The initial results are promising,” says study co-author Emily Hadley, a research data scientist at the research nonprofit RTI International.
But, experts say, no one should dismiss reinfections as harmless. The study did not directly address a possibility that has been raised in some previous research, including some conducted by Al-Aly: that the risks of complications including heart, lung, and brain damage may pile up with each additional infection, whether or not someone is diagnosed with Long COVID.
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“All studies that explore risks of reinfection should be through the lens of cumulative risk,” says David Putrino, who researches Long COVID at New York’s Mount Sinai health system but was not involved in either new study. Putrino also notes that health records—the basis of both new studies—are imperfect data sources, since they don’t capture the experiences of patients who don’t seek health care, nor those who are not officially diagnosed with Long COVID.
Even when focusing on people who were officially diagnosed with Long COVID, the new reinfections study still raises some alarms, says Dr. David Goff, a member of the NIH’s RECOVER oversight committee. For him, the key takeaway isn’t that reinfections are less likely to result in Long COVID; it’s that some people still develop Long COVID, even after second infections.
“Even if you believe that the risk of developing Long COVID is a little less after a reinfection than after initial infection, it’s still there,” Goff says. “It’s not zero.”
Similarly, even in the best-case scenario in Al-Aly’s study—vaccinated adults who contracted COVID-19 during the Omicron era—more than 3% still ended up with Long COVID, which translates to potentially millions of new cases at a national level.
Taken together, the studies suggest that changes in the virus, population immunity, and medical care are chipping away at the risk of Long COVID, but not eliminating it completely. Whether one focuses on the good news or bad news depends largely on perspective and personal risk tolerance, says Akiko Iwasaki, an immunobiologist and Long COVID researcher from the Yale School of Medicine who was not involved in either new study.
Findings like these could be seen as reason to worry less. Or, they could be seen as proof that Long COVID—while perhaps not the threat it once was—continues to affect new people all the time. “Knowing how devastating Long COVID can be,” Iwasaki says, “I tend to be in the more cautious camp.”
