The most recent COVID-19 booster shot reduces adults' risk of moderate or severe COVID by more than half, according to a new nationwide data study from September 2023 through January 2024, a period of JN.1 variant dominance.

The new study is one of the first to evaluate protection provided by the updated shot against COVID-19-associated emergency department and urgent care visits (markers for moderate disease) and against hospitalizations (a marker for severe disease), in individuals 18 and older, due to JN.1, the most recently predominant strain of COVID.

Halving your risk of needing to visit an E.D. or urgent care center or to be treated in the hospital for COVID is significant. As an informatician I want to highlight that the data we analyzed came from different populations and geographic locations, adults of all ages and the most recent COVID strain. This analysis strongly supports the benefit of getting a booster shot and as a clinician, I encourage my patients to do so."

Shaun Grannis, M.D., M.S., study co-author, Regenstrief Institute vice president for data and analytics and professor at Indiana University School of Medicine

"These are encouraging findings," said study co-author Brian Dixon, PhD, MPA, interim director of Regenstrief Institute's Clem McDonald Center for Biomedical Informatics and professor at Indiana University Richard M. Fairbanks School of Public Health. "These estimates of vaccine effectiveness are what we would expect for an annual booster designed for an endemic virus that continues to evolve. We looked at a longer time period than similar studies in Europe, and we found good performance. Yet we do need to be alert to the presumed waning of the updated booster's effectiveness, which we have seen in earlier COVID-19 vaccines. Americans should expect the CDC to recommend future boosters, likely on an annual schedule."

These findings of protection against moderate and severe disease provided by the booster in this large study are consistent with those of an earlier, small scale study of individuals seen for testing at a pharmacy. That study did not include hospitalized patients.

The authors of the new study, co-authored by Drs. Grannis and Dixon, concluded, "In this analysis of updated COVID-19 VE [vaccine effectiveness], receipt of an updated COVID-19 vaccine dose provided protection against COVID-19-associated ED/UC [emergency department/critical care] visits and hospitalizations among immunocompetent adults. CDC will continue monitoring VE of updated COVID-19 vaccines. All adults should stay up to date with recommended COVID-19 vaccines, including receiving a dose of updated vaccine."