New evidence on the 2024-2025 Covid boosters
A large observational study of US military veterans found that the updated Covid-19 vaccines released for the 2024-2025 season helped reduce severe illness, hospitalizations, and deaths among those who contracted Covid-19 after vaccination. The findings, published in The New England Journal of Medicine, come as health officials and clinicians continue to assess the real-world impact of updated boosters in a country where Covid-19 remains a major public health concern.
Study design and participants
Researchers analyzed data from a substantial cohort of veterans, comparing two groups: 164,132 individuals who received a 2024-2025 Covid booster in addition to a flu shot, and 131,839 individuals who received only the flu shot. Most participants were aged 45 and older, a demographic that has faced higher risks from Covid-19 in earlier stages of the pandemic. The vaccines involved were the two main mRNA vaccines available in the United States, Moderna and Pfizer/BioNTech, both adjusted to circulating variants at the time of vaccination.
Key findings: meaningful protection remains
The analysis showed that, over a six-month period, receipt of the Covid booster alongside the flu vaccine was associated with a substantial reduction in several severe outcomes when compared with vaccination against flu alone. Specifically, veterans who were boosted and experienced Covid had a 29% lower rate of emergency department visits, a 39% reduction in hospitalizations, and a striking 64% decrease in deaths attributable to Covid-19 complications.
Experts noted that the absolute benefit was modest in some respects because the overall incidence of severe Covid-19 outcomes had declined from earlier in the pandemic. Still, the study suggests that the boosters continue to confer important protection against serious disease, even as the virus evolves and population immunity rises from prior infections and vaccinations.
Interpretation from experts
Dr. Jesse Goodman of Georgetown University Medical Center, who was not involved in the research, commented that the vaccines provide additional, meaningful protection against hospitalization and death. He emphasized that while no intervention is perfect, the observed benefits remain clinically relevant for mid- to older-aged adults, particularly those with preexisting conditions.
Dr. Eric Rubin, editor-in-chief of NEJM, pointed out that vaccination effects tend to wane somewhat over time, but still offer attractive protection in real-world settings where disease severity has declined. He noted that the absolute risk reductions reflect the current lower baseline risk, yet they remain meaningful for individuals who require prevention of serious outcomes.
Limitations and context
The researchers cautioned that the study is observational and thus cannot establish causation. Participants were not randomized to receive the booster, and residual confounding could influence results. Nevertheless, the large sample size and real-world setting strengthen confidence in the observed associations. The findings align with prior observational work suggesting enduring, though reduced, vaccine effectiveness against severe outcomes in a population with substantial prior exposure and vaccination history.
What this means for vaccination decisions
As the epidemiology of Covid-19 continues to evolve, public health officials have stressed that vaccines remain a valuable tool for reducing serious illness. For middle-aged and older adults, especially those with chronic health conditions, boosters can lower the risk of emergency care, hospitalization, and mortality associated with Covid-19.
Vaccination decisions continue to balance individual risk, local transmission, and the broader public health goal of preventing severe disease. Health authorities recommend discussing personal risk factors with a clinician to determine the most appropriate vaccination plan for the current season.
