https://www.sciencedaily.com/releases/2021/09/210902101114.htm

The letter's authors report that the effectiveness of both the Pfizer and Moderna mRNA COVID-19 vaccines significantly waned over time. Both vaccines were granted emergency use authorization by the Food and Drug Administration in December 2020, with vaccinations of the UC San Diego Health work force beginning the same month for health care workers with direct, patient-facing duties.

In the letter, the authors note that from March through June 2021 vaccine effectiveness against symptomatic infection was estimated to exceed 90 percent; by July, however, it had fallen to approximately 65 percent.