Tartof SY, Slezak JM, Fischer H, et al. - Among members of the health-care organization Kaiser Permanente Southern California (CA, USA), the overall and variant-specific effectiveness of BNT162b2 (tozinameran, Pfizer–BioNTech) against SARS-CoV-2 infections was examined and COVID-19-related hospital admissions were determined by time since vaccination.

• A retrospective cohort study assessing 4,920,549 individuals for eligibility (≥ 12 years) and identifying 3,436,957 patients for inclusion (median age 45 years [IQR 29–61]; 1,799,395 [52·4%] female and 1,637,394 [47·6%] male).

• BNT162b2 was supported to have high effectiveness against hospital admissions up until around 6 months after being fully vaccinated, even in the face of widespread dissemination of the delta variant.

• For fully vaccinated individuals, there appeared 73% effectiveness against SARS-CoV-2 infections and 90% effectiveness against COVID-19-related hospital admissions.

• Waning immunity with time could be the primary cause of the reduction in vaccine effectiveness against SARS-CoV-2 infections over time rather than the delta variant escaping vaccine protection.