Last year's updated COVID-19 vaccines helped prevent severe outcomes including hospitalizations and deaths, according to data from a large study of U.S. military veterans published on Wednesday.

Vaccinated veterans who developed COVID after receiving the 2024-2025 boosters from Moderna or Pfizer/BioNTech were also less likely to visit the emergency room for complications, compared with unvaccinated COVID patients, researchers reported in The New England Journal of Medicine.

The researchers tracked 164,132 veterans who simultaneously received a 2024-2025 COVID booster and a flu shot, and 131,839 who received only the flu vaccine.

The vast majority of participants were at least 45 years old, and virtually all who received a COVID shot got one of the two approved mRNA-based vaccines that have faced renewed scrutiny from U.S. Health Secretary Robert F. Kennedy Jr., who has questioned their safety and efficacy, contrary to scientific evidence.

MEANINGFUL CLINICAL BENEFIT

"The vaccines are still providing additional, not perfect, protection against meaningful outcomes, including hospitalization and death, even though such severe outcomes are now much less common overall than early in the pandemic," said Dr. Jesse Goodman of Georgetown Medical Center in Washington, D.C., who was not involved in the study.

Over six months, veterans who received the COVID and flu vaccines had a 29% decrease in emergency department visits, a 39% decrease in hospitalizations, and a 64% decrease in deaths compared to those who received only the flu vaccine.

The pattern was similar regardless of age or the presence of major chronic medical conditions.

In absolute terms, the added impact of the COVID shot was small, at least in part because versions of the virus circulating at the time cause milder illness, and previous infections and vaccinations have led to greater immunity, the researchers said.

Vaccination resulted in 18.3 fewer emergency department visits, 7.5 fewer hospitalizations, and 2.2 fewer deaths per 10,000 patients, they estimated.

Because rates of COVID-related serious disease and death have dropped dramatically over time, the extra protection provided by the vaccine is a lot smaller than it once was, said Dr. Eric Rubin, NEJM editor-in-chief.

"Given what we know about the risk of vaccination in this (middle-age and older) population, which is extremely low, these data suggest that, at least at that point when the study was performed, vaccination remained an attractive option," Rubin said.

Goodman, a former chief scientist at the U.S. Food and Drug Administration, said all recent observational studies, including this one, "support the vaccines still having meaningful effectiveness on significant outcomes."

Vaccine effectiveness appeared to wane modestly during the six-month study, the researchers found.

The study was not a randomized trial and so it cannot prove the COVID vaccines prevented the more severe outcomes, they noted.