Incidence of COVID-19 in HCWs after single dose of the Moderna vaccine

Editor's Note

This study from the VA Boston Healthcare System finds an association between receipt of Moderna’s mRNA-1273 vaccine and a reduction in COVID-19 infections in healthcare workers (HCWs) beginning 8 days after the first dose.

In this analysis of 4,028 HCWs, 3,367 were vaccinated during the study period. Of these, COVID-19 infection was identified in 107—39 vaccinated and 68 unvaccinated.

Among the 39 vaccinated COVID-19-positive HCWs, 26 received dose 1 before December 29, 2020. Vaccine clinical effectiveness was 50.3% for the entire 42-day follow-up period, 77.5% for days 8 through 42, and 95.0% for days 15 through 42. Clinical effectiveness was similar when the analysis was limited to the first 28 days, thereby excluding second-dose effects.

The first-dose risk reduction of 95% after day 14 shows the potential for vaccination with mRNA-1273 to rapidly mitigate surges of COVID-19 infections in HCWs, the authors say.