Vaccine Effectiveness against SARS-CoV-2 Variant P.1 in Nursing-Facility Residents, Washington, USA, April 2021

Area of Science:

• Infectious Diseases
• Vaccinology
• Epidemiology

Background:

• The SARS-CoV-2 P.1 (Gamma) variant emerged as a significant global concern.
• Skilled nursing facilities (SNFs) are vulnerable settings for infectious disease outbreaks.
• Vaccination is a primary strategy to mitigate SARS-CoV-2 transmission and severity.

Purpose of the Study:

• To evaluate the effectiveness of mRNA vaccines against the SARS-CoV-2 P.1 (Gamma) variant.
• To assess vaccine effectiveness in a real-world outbreak setting within a SNF.
• To compare P.1 variant vaccine effectiveness to that of previous SARS-CoV-2 variants.

Main Methods:

• Retrospective analysis of a SARS-CoV-2 P.1 (Gamma) variant outbreak in a Washington, USA SNF in April 2021.
• Calculation of vaccine effectiveness (VE) using a confirmed case-control or cohort approach.
• Comparison of VE against P.1 infection with previously reported VE for other SARS-CoV-2 variants.

Main Results:

• An outbreak of the SARS-CoV-2 P.1 (Gamma) variant occurred in a SNF.
• Two doses of mRNA vaccines demonstrated 75.0% effectiveness (95% CI 44.5%-88.7%) against P.1 infection in this cohort.
• The observed vaccine effectiveness was similar to that reported for other pre-Delta variants in long-term care residents.

Conclusions:

• mRNA vaccines provide substantial protection against the SARS-CoV-2 P.1 (Gamma) variant, even during an outbreak in a SNF.
• Vaccine effectiveness against P.1 in SNF residents is comparable to earlier variants, supporting ongoing vaccination efforts.
• These findings underscore the importance of high vaccination coverage in long-term care facilities to prevent severe outcomes from emerging variants.