While mRNA vaccines against COVID-19 have been found to be safe and effective for the general population, in-depth evidence about safety and effectiveness for older adults and individuals with chronic health conditions is more limited. To address that gap, a team led by Brown University researchers conducted the largest head-to-head comparison study of the two mRNA vaccines approved by the U.S. Food and Drug Administration--the Moderna and Pfizer-BioNTech vaccines. The results, published on August 2, 2023 in JAMA Network Open, showed that for older adults, the Moderna vaccine was associated with a slightly lower risk of adverse events than the Pfizer-BioNTech vaccine. The open-access article is titled “Comparative Risks of Potential Adverse Events Following COVID-19 mRNA Vaccination Among Older US Adults.” “The results of this study can help public health experts weigh which mRNA vaccine might be preferred for older adults and older subgroups, such as those with increased frailty,” said lead study author Daniel Harris, PhD, an epidemiologist and research scientist in the Center for Gerontology and Healthcare Research at the Brown University School of Public Health.