A large study of COVID-19 disease following vaccination and booster, published in the Journal of the American Medical Association (JAMA), reports surprisingly low incidence, especially in individuals younger than 65 years of age with no high-risk conditions.

Hospitalizations for COVID-19 disease among individuals who had received vaccines and boosters occurred almost exclusively among high-risk patients including older adults and adults of all ages with certain comorbidities or immunocompromising conditions.

This retrospective study of 1.6 million patients at Veterans Health Administration facilities, the largest integrated health care system in the U.S., found the incidence—new cases over time—of hospitalization for COVID-19 pneumonia or death was 8.9 per 10,000 persons who had been vaccinated and boosted. While the incidence for vaccinated and boosted older adults with comorbid or immunocompromising conditions was tenfold higher, it was still a relatively low rate of occurrence of bad outcomes.

"This is remarkable, good news about the power and effectiveness of receiving COVID-19 boosting for all groups," said co-author Regenstrief Institute and Roudebush VA Medical Center research scientist Dawn Bravata, M.D., who led the study's chart review core. "With the power of VA data, we had such complete information on a large number of patients including many who are older and those who have comorbidities or are immunocompromised, that we could examine this issue thoroughly.

"These results, from a period of Delta and Omicron predominance, should encourage people to get vaccinated and boosted," said Dr. Bravata, who is also a professor of medicine at Indiana University School of Medicine.

To avoid misclassification of death or other serious outcomes due to COVID rather than to other health issues, the study authors rigorously evaluated patient medical records for breakthrough COVID-19, COVID-19 pneumonia and death, as opposed to simply considering all hospitalizations among patients with a positive COVID-19 lab test.

"Early in the pandemic, many researchers, including our own group, published studies about COVID-19 hospitalizations. But we're in a different era now when patients who are admitted to the hospital with a non-COVID illness are screened; some of whom will test positive. Evaluating outcomes such as COVID-19 pneumonia or mortality—as opposed to simply considering all hospitalization—makes more sense," said Dr. Bravata.