During the first two years of the COVID-19 pandemic, researchers observed a significantly lower rate of long COVID among vaccinated individuals. This finding comes from a comprehensive new study, which offers robust evidence that vaccines play a crucial role in reducing the risk of developing long COVID.
The study focused on individuals in the United States who contracted COVID-19 during the initial two years of the pandemic. It revealed that vaccinated people were much less likely to develop long COVID compared to those who were unvaccinated. Medical experts have long suggested that vaccines help mitigate the risk of long COVID, primarily by preventing severe illness during the acute phase of infection. Since severe infections are more likely to result in long-term symptoms, reducing the severity of the initial infection also lowers the likelihood of long COVID.
However, even individuals with mild infections can develop long COVID. The study, published in The New England Journal of Medicine, highlighted that vaccination does not completely eliminate the risk of long COVID, a condition that continues to impact millions of people in the United States. Dr. Clifford Rosen, a senior scientist at the MaineHealth Institute for Research, noted in an accompanying editorial that there remains a residual risk of long COVID among vaccinated individuals, suggesting that new cases may persist.
The research analyzed medical records from millions of patients within the Department of Veterans Affairs health system, including nearly 450,000 individuals who had contracted COVID-19 between March 1, 2020, and January 31, 2022, as well as approximately 4.7 million people who were not infected during that period. The study population primarily consisted of veterans, who were less diverse than the general American population. About 91 percent of the participants were male, nearly three-fourths were white, and the average age was 64.
Researchers estimated the percentage of COVID-19 patients who experienced long COVID symptoms one year after infection. The lowest incidence of long COVID, 3.5 percent, was observed among vaccinated individuals infected between mid-December 2021 and January 2022. In contrast, 7.8 percent of unvaccinated patients infected during the same period developed long COVID.
Dr. Ziyad Al-Aly, the study’s lead author and the chief of research and development at the V.A. St. Louis Health Care System, attributed much of this decline to vaccination. He emphasized that vaccine effectiveness diminishes over time and stressed the importance of keeping up with yearly vaccine shots to maintain protection against long COVID. Dr. Al-Aly cautioned against complacency, warning that neglecting vaccinations could lead to a resurgence in long COVID cases.
To ensure accuracy, the researchers accounted for other potential causes by comparing symptoms in uninfected individuals with similar conditions, such as cancer, which can also cause fatigue and brain fog. By subtracting the rate of these symptoms in uninfected people from those in infected patients, they calculated the percentage of symptoms attributable to long COVID.
The study spanned the emergence of the virus and the rise of the Delta and Omicron variants, comparing results between vaccinated and unvaccinated patients. Among unvaccinated individuals infected during the Delta variant’s dominance (June 19 to December 18, 2021), the long COVID rate decreased slightly from 10.4 percent to 9.5 percent. During the Omicron wave (December 19, 2021, to January 31, 2022), this rate further declined to 7.8 percent.
Vaccinated individuals showed significantly lower rates of long COVID. The authors attributed approximately 72 percent of this reduction to vaccines, with 5.3 percent of those infected during the Delta period and 3.5 percent during the Omicron period developing long COVID. Dr. Al-Aly noted that while these rates are lower, they are not insignificant. Given the large number of ongoing infections, even a 3.5 percent rate could result in millions of additional long COVID cases.
The researchers did not analyze more recent periods, but a Centers for Disease Control and Prevention survey estimated that 5.3 percent of U.S. adults (about 13.7 million people) currently suffer from long COVID. The study also found that while cardiovascular and kidney problems associated with long COVID decreased over time, gastrointestinal, metabolic, and musculoskeletal issues increased during the Omicron era among unvaccinated individuals, likely due to changes in the virus and other factors.