Effectiveness Of Pfizer-Biontech And Moderna Vaccines In Preventing Sars- Cov-2 Infection Among Nursing Home Residents Before And During Widespread Circulation Of The Sars-Cov-2 B.1.617.2 (Delta) Variant National Healthcare Safety Network, March 1-August 1, 2021

What is already known about this topic?Early observational studies among nursing home residents showed mRNA vaccines to be 53% to 92% effective against SARS-CoV-2 infection.What is added by this report? Two doses of mRNA vaccines were 74.7% effective against infection among nursing home residents early in the vaccination program (March-May 2021). During June-July 2021, when B.1.617.2 (Delta) variant circulation predominated, effectiveness declined significantly to 53.1%.What are the implications for public health practice? Multicomponent COVID-19 prevention strategies, including vaccination of nursing home staff members, residents, and visitors, are critical. An additional dose of COVID-19 vaccine might be considered for nursing home and long-term care facility residents to optimize a protective immune response.