Tartof et al. conducted a retrospective cohort study to evaluate the effectiveness of the BNT162b2 tozinameran Pfizer–BioNTech vaccine against SARS-CoV-2 infection and COVID-19 hospitalizations among individuals aged 12 years or older who were members of Kaiser Permanente Southern California. The study, which took place between December 2020 and August 2021, included over 3.4 million participants (52% female) and found that overall effectiveness against infection was 73% among those fully vaccinated and 90% overall against hospital admission. Effectiveness against infection waned with time, from 88% in the month after vaccination to 47% five months later; however, overall adjusted effectiveness against hospitalization remained approximately the same over time (87% effectiveness within one month compared to 88% effectiveness within five months of full vaccination).