Key findings from the study:
- Obtaining two vaccine doses remains the most effective way to ensure protection against the COVID-19 Delta variant of concern dominant in the UK today.
- With Delta, 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.
- 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
- Using 4,091,537 RT-PCR results from 482,677 individuals, we show substantial variation in which of 60 demographic and behavioural characteristics were associated with swab positivity over July 2020 to July 2021.
- Population-level demographic and behavioural surveillance can be a valuable tool in identifying the varying characteristics driving current SARS-CoV-2 positivity, allowing monitoring to inform public health policy.
- Within the COVID-19 Infection Survey, recruiting representative households across the UK general population, SARS-CoV-2-associated symptoms varied by viral variant, vaccination status and demographics. However, differences are modest and do not currently warrant large-scale changes to targeted testing approaches