BACKGROUND: Coronavirus disease 2019 (COVID-19) outbreaks often occur in nursing homes and prompt frequent surveillance testing for SARS-CoV-2. A single dose of the BNT162b2 vaccine reduces viral load and transmission. In this study, we describe the real-world efficacy of BNT162b2 single-dose vaccination during a COVID-19 outbreak at a Veterans Affairs Community Living Center (CLC). METHODS: From 12/2/20-5/14/21, twice weekly antigen testing was used to detect COVID-19 among 146 residents at the CLC. Residents without a prior history of COVID-19 who agreed to immunization were vaccinated with the BNT162b2 vaccine on 12/16/20 and 1/6/21. Single-dose vaccine efficacy was determined for days 1-21 and days 14-21 after the first vaccine dose. RESULTS: The outbreak occurred from 12/2/20-1/7/21 with an attack rate of 30.8% (45/146); 46.7% (21/45) of the cases were due to asymptomatic COVID-19. One unit accounted for 77.8% (35/45) of the cases. In the vaccine analysis, 116 residents were a median age of 74.5 years and 93.1% (108/116) had >/= 1 comorbid condition. Between the first and second dose, 15.5% (15/97) of vaccinated residents, and 21.2% (4/19) of unvaccinated residents developed COVID-19 (p=0.81). One week after the second dose, no cases of COVID-19 occurred. CONCLUSIONS: Albeit limited by the small numbers, a single dose of the BNT162b2 vaccine was not efficacious at preventing COVID-19 during this nursing home outbreak.