However, Delta infections after two vaccine doses had similar peak levels of virus to those in unvaccinated people; with the Alpha variant, peak virus levels in those infected post-vaccination were much lower. Two doses of Pfizer-BioNTech have greater initial effectiveness against new COVID-19 infections, but this declines faster compared with two doses of Oxford-AstraZeneca. It is the first to show how protection against COVID-19 infections changes over time following second vaccinations in a large group of adults from the general population. About the studyReleased today as a pre-print, the study compares protection from infections from COVID-19 vaccines before and after 17 May 2021, when Delta became the main variant in the UK. Participants on the Covid Infection Survey have helped us to learn a huge amount about the virus and I would like to thank them all for their continued participation – we are very grateful.’
