The latest findings of an ongoing national study of COVID-19 immunity in households across the UK has found that the Pfizer-BioNTech and Oxford-AstraZeneca vaccines offer good protection against new infections of the Delta variant of concern, but that effectiveness is reduced compared with the Alpha variant.
The COVID-19 infection survey, led by Oxford University and the Office for National Statistics, found that getting two vaccine doses remains the most effective way to ensure protection against the Delta, the dominant variant in the UK today.
The findings of the latest study – Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK – have been published as a pre-print.
The Chief Investigator on the study is Professor Sarah Walker, the NIHR Oxford BRC’s Co-theme Lead for Antimicrobial Resistance and Modernising Microbiology
The key findings from the study were:
- Obtaining two vaccine doses remains the most effective way to ensure protection against the COVID-19 Delta variant of concern
- With the Delta variant, Pfizer-BioNTech and Oxford-AstraZeneca vaccines still offer good protection against new infections, but effectiveness is 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.
- 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.
Other findings included:
- A single dose of the Moderna vaccine has similar or greater effectiveness against the Delta variant as single doses of the other vaccines.
- 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. Results suggest that after four to five months effectiveness of these two vaccines would be similar – however, long-term effects need to be studied.
- The time between doses does not affect effectiveness in preventing new infections, but younger people have even more protection from vaccination than older people.