On Aug. 19, 2021, the University of Oxford reported that obtaining two vaccine doses remained the most effective way to ensure protection against the COVID-19 Delta variant of concern dominant in the UK.

Conducted in partnership with the Office of National Statistics and the Department for Health and Social Care, the study found that with Delta, Pfizer-BioNTech and Oxford-AstraZeneca vaccines still offered good protection against new infections, but effectiveness was reduced compared with Alpha.

Two doses of either vaccine still provided at least the same level of protection as having had COVID-19 before through natural infection; people who had been vaccinated after already being infected with COVID-19 had even more protection than vaccinated individuals who had not had COVID-19 before.