CDC-blocked COVID-19 vaccine study published in JAMA Network Open

A study examining the effectiveness of the 2025-26 COVID-19 vaccine was published Tuesday in the journal JAMA Network Open after federal health officials blocked its inclusion in a March edition of the CDC's Morbidity and Mortality Weekly Report. The study was conducted by CDC researchers and colleagues in California, Colorado, Georgia, Indiana, Maryland, Minnesota, New York, Oregon, Texas, and Utah.

It measured vaccine performance among adults aged 18 and older without weakened immune systems during the fall and winter of 2025. Researchers estimated the updated vaccines lowered the risk of COVID-19 hospitalization by 55 percent and the risk of emergency department or urgent care visits by 50 percent compared with people who did not receive the shot.

Study methodology and limits The authors noted the study did not account for prior COVID-19 infection or earlier vaccinations, so the results may reflect added protection from the 2025-26 formulation on top of existing immunity. They also listed several limitations, including incomplete vaccine records and low numbers of vaccinations and hospitalizations.

The study used a test-negative design, an observational method that compares vaccination status between patients who test positive and those who test negative for the virus.

CDC review process An HHS spokesperson stated that when questions arise about methodology, officials address them directly and prefer careful review to ensure analyses are sound. The same statement said the CDC evaluates evidence using rigorous methods and subjects its work to scientific scrutiny before publication.

The study was originally scheduled for the CDC's weekly report in March. It appeared instead in JAMA Network Open on Tuesday.