Two doses of the mRNA BNT162b2 vaccine reduce severe outcomes, viral load and secondary attack rate: evidence from a SARS-CoV-2 Alpha outbreak in a nursing home in Germany, January-March 2021

A SARS-CoV-2 Alpha outbreak was detected in a nursing home after residents and staff had completed vaccination with BNT162b. In a retrospective cohort study, we estimated an age-adjusted vaccine effectiveness of 88% [95% confidence interval (95%CI) 41-98%] against hospitalization/death. Ct values at diagnosis were higher with longer intervals since the second vaccination [>21 vs. ≤21 days: 4.82 cycles, 95%CI: 0.06-9.58]. Secondary attack rates were 67% lower in households of vaccinated [2/9 (22.2%)] than unvaccinated infected staff [12/18 (66.7%); p=0.046]. Vaccination reduced the risk of severe outcomes, Ct values and transmission, but not fully. Non-pharmaceutical interventions remain important for vaccinated individuals.