Resurgence of COVID-19 infection in fully vaccinated HCWs in San Diego

Editor's Note

This study finds that fully vaccinated healthcare workers (HCWs) at University of California San Diego Health experienced a rapid increase in COVID-19 infections from June to July 2021.

Vaccinations began in mid-December, and by March 2021, 76% of HCWs were fully vaccinated. This rose to 83% by July.

From March 1 to July 31, 2021, a total of 227 HCWs tested positive for COVID-19, and 130 of those were fully vaccinated. 

Vaccine effectiveness exceeded 90% from March through June but fell to 65.5% in July.

In HCWs completing vaccination in January or February, the COVID-19 attack rate was 6.7 per 1,000, whereas the attack rate was 3.7 per 1,000 in those who completed vaccination from March through May. Among unvaccinated HCWs, the July attack rate was 16.4 per 1,000.

The dramatic change in vaccine effectiveness is likely due to the rapid emergence of the Delta variant in mid-April and waning immunity over time, compounded by the end of California’s mask mandate on June 15, the researchers say.