Vaccine effectiveness against symptomatic Covid-19 with the delta variant decreased with ChAdOx1-S and the BNT162b2 vaccine after 20 weeks of second dose. However, effectiveness against hospitalization and death did not decrease much at 20 weeks.

The wening was more in

ChAdOx1-S vaccine as compared to BNT162b2
Persons 65 years of age or older
Clinically extremely vulnerable group
Persons 40 to 64 years of age with underlying medical conditions
Effectiveness of BNT162b2 vaccine during proxy omicron period was 70%.

Reference: NEJM

DOI: 10.1056/NEJMc2119270
DOI: 10.1056/NEJMoa2115481