Very low incidence of severe COVID-19 following vaccination and booster, large study reports

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 healthcare 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.

Authors of"Incidence of Severe COVID-19 Illness Following Vaccination and Booster With BNT162b2, mRNA-1273, and Ad26.COV2.S Vaccines" are J. Daniel Kelly, M.D., PhD, San Francisco VA Medical Center and University of California; San Francisco; Samuel Leonard, M.S., San Francisco VA Medical Center; Katherine J. Hoggatt, PhD, San Francisco VA Medical Center and University of California, San Francisco; W. John Boscardin, Ph.D.; University of California, San Francisco; Emily N. Lum, MPH, San Francisco VA Medical Center; Tristan A. Moss-Vazquez, B.A., San Francisco VA Medical Center; Raul Andino, PhD, University of California, San Francisco; Joseph K. Wong, M.D., San Francisco VA Medical Center and University of California, San Francisco; Amy Byers, PhD, San Francisco VA Medical Center; Dawn M. Bravata, M.D., Richard Roudebush VA Medical Center (Indianapolis), Regenstrief Institute and Indiana University School of Medicine; Phyllis C. Tien, M.D., San Francisco VA Medical Center and University of California, San Francisco; Salomeh Keyhani, M.D., MPH, San Francisco VA Medical Center and University of California, San Francisco.

This work was supported by VA Clinical Science Research and Development grant I01 CX002417 and the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, grant K23 AI146268.