Cohort study: Pfizer vaccine effectiveness against any infections declined from 88% during the first month after full vaccination to 47% after 5 months. Vaccine effectiveness against hospital admissions remained high; 87% within 1 month, and 88% at 5 months after full vaccination, with no significant waning.

Effectiveness of mRNA BNT162b2 COVID-19 vaccine up to 6 months in a large integrated health system in the USA: a retrospective cohort study – The Lancet

Commentary: Expert reaction to study on Pfizer-BioNTech vaccine effectiveness up to 6 months – Science Media Centre

Commentary on Twitter

Study of 3.4 million people @aboutKP @TheLancet

Vaccine efficacy against infections:
– First month post: 88%
– 5 months post: 47%

But vaccine efficacy against hospitalization (Figure):
– First month post: 87%
– 5 months post: 88 %https://t.co/1Gse0FKpoI pic.twitter.com/p9wyiaWGeg

— Vincent Rajkumar (@VincentRK) October 4, 2021