A new study suggests that the 2025-26 COVID-19 vaccine helps protect against serious illness by reducing the risk of hospitalization and emergency department/urgent care (ED/UC) visits, adding protection for a population with significant existing immunity from previous infections and vaccinations.
The study, published today in JAMA Network Open, found that adults who received the updated vaccine were about 50% less likely to require ED/UC treatment for COVID and 55% less likely to be hospitalized than those who did not receive the vaccine.
The study’s findings were suppressed from publication earlier this year by the Centers for Disease Control and Prevention (CDC). At the time, interim CDC Director Jay Bhattacharya, MD, PhD, expressed concerns about the method used in the study to calculate vaccine effectiveness (VE), despite the method (test-negative design) having been used for decades as part of routine flu vaccine monitoring and the CDC’s own VE estimates, according to a commentary published alongside the study.
Booster augments previous immunity
For the study, researchers led by a team from the Centers for Disease Control and Prevention (CDC) analyzed data from more than 111,000 adults across 253 EU/UCs and 179 hospitals in seven states from September through December 2025. They compared patients who tested positive for COVID with those who tested negative and identified whether they had received the 2025-26 vaccine.
Overall, VE against COVID-related ED/UC visits was estimated at 50%. Protection against hospitalization was 55%.
Among adults ages 65 and older, VE was 48% against ED/UC visits and 53% against hospitalization. Older adults face the highest risk of severe outcomes from COVID.
The findings in this study demonstrate the added benefit of 2025-2026 COVID-19 vaccination irrespective of protection conferred by previous COVID-19 vaccination or SARS-CoV-2 infection.
While hospitalization rates during the first part of the 2025-26 respiratory virus season were lower than in previous years, COVID-related severe illness remains a significant issue. There were an estimated 390,000 to 550,000 COVID-related hospitalizations in the United States from October 2024 to September 2025, with the highest hospitalization rate reported among adults 65 and older.
The protective benefits of the 2025-26 booster bolstered previous immunity. “The findings in this study demonstrate the added benefit of 2025-2026 COVID-19 vaccination irrespective of protection conferred by previous COVID-19 vaccination or SARS-CoV-2 infection,” the authors write.
59% lower risk of medically attended illness
The findings align with a separate study conducted in France, Germany, Ireland, Italy, and Spain by the Vaccine Effectiveness, Burden and Impact Studies (VEBIS) Primary Care Vaccine Effectiveness Group.
For the study, published last week in JAMA Network Open, researchers examined the effectiveness of 2025-26 COVID vaccines in older adults who sought care for respiratory illnesses from September 2025 to January 2026.
The findings suggest that vaccination reduced the risk of symptomatic COVID infection that required a healthcare visit by 59%, although with uncertainty (95% confidence interval [CI], 14% to 83%), among older adults during the first two months after vaccination.
Protection waned slightly over time—VE was 64% (95% CI, 8% to 89%) 14 to 41 days after vaccination and 52% (95% CI, −39% to 89%) 42 to 83 days after vaccination, again with uncertainty.
Vaccine uptake low in both studies
In both studies, vaccine uptake was low. In the study led by the CDC, only 11% of patients included in the analysis received a 2025-26 booster, and only 6% of patients who tested positive for COVID in the European study had been vaccinated, compared with 19% of those who tested negative.
“The low uptake of vaccines, which showed substantial short-term effectiveness, suggests missed opportunities for preventing symptomatic COVID-19 among unvaccinated vulnerable groups,” write the authors of the European study.
‘Science was never the issue’
The findings from the US-based study were scheduled to be published in the CDC’s Morbidity and Mortality Weekly Report (MMWR) in March when Bhattacharya halted publication, citing methodological concerns.
In the commentary, Natalie Dean, PhD, associate professor in the Department of Epidemiology at Emory Rollins School of Public Health, acknowledges that test-negative design “has limitations,” but that scientists don’t ignore those limitations.
“Epidemiologic methods journals are filled with studies seeking to better characterize and reduce bias in TND [test-negative design] analyses, including contributions from the study’s authors,” she says. “It is standard for TND studies to be accompanied by extensive sensitivity analyses, assessing the potential for bias, testing for residual confounding, and checking the robustness of the interpreted findings.”
“Science was never the issue,” study coauthor Michelle Barron, MD, tells the Washington Post in a follow-up piece published this week announcing the findings' publication. She suspects the study was suppressed because of Health and Human Services Secretary Robert F. Kennedy Jr.’s anti-vaccine agenda.
Specifically, Kennedy has focused on limiting access to the COVID vaccine. “Certainly it was within [the CDC’s] purview to keep it out, for whatever reason, but it was clearly not for scientific reasons that the study was withheld from publication in the MMWR,” Barron concludes.
