In the first head-to-head comparison of the Pfizer/BioNTech and Moderna mRNA COVID-19 vaccines, Moderna edged out its competition with a 21% lower risk of infection and a 41% lower risk of hospitalization over 24 weeks, according to a study yesterday in the New England Journal of Medicine (NEJM).

A team led by researchers from Harvard University and the US Department of Veterans Affairs (VA) analyzed the electronic medical records of veterans nationwide, almost all of whom received two doses of either the Pfizer or Moderna COVID-19 vaccine from Jan 4 to May 14, 2021. The study period was dominated by the SARS-CoV-2 Alpha (B117) variant.

"Both vaccines are incredibly effective, with only rare breakthrough cases," said study coauthor Juan Casas, MD, PhD, an epidemiologist at Brigham and Women's Hospital in Boston and a Harvard associate professor, in a VA news release. "But regardless of the predominant strain—Alpha earlier and then Delta later—Moderna was shown to be slightly more effective."