The
effectiveness of BNT162b2, ChAdOx1, and
mRNA-1273
vaccines against new SARS-CoV-2 infections requires continuous re-evaluation, given the increasingly dominant
Delta variant. We investigated the
effectiveness of the
vaccines in a large
community-based
survey of randomly selected
households across the UK. We found that the
effectiveness of BNT162b2 and ChAd0x1 against any
infections (new
PCR positives) and
infections with symptoms or high
viral burden is reduced with the
Delta variant. A
single dose of the
mRNA-1273
vaccine had
similar or greater
effectiveness compared to a
single dose of BNT162b2 or ChAdOx1.
Effectiveness of two doses remains at least as great as
protection afforded by prior natural
infection. The dynamics of
immunity following second doses differed significantly between BNT162b2 and ChAdOx1, with greater initial
effectiveness against new
PCR-positives but faster declines in
protection against high
viral burden and symptomatic
infection with BNT162b2. There was no evidence that
effectiveness varied by dosing interval, but
protection was higher among those vaccinated following a prior
infection and younger
adults. With
Delta,
infections occurring following two
vaccinations had
similar peak
viral burden to those in unvaccinated individuals.
SARS-CoV-2 vaccination still reduces new
infections, but
effectiveness and attenuation of peak
viral burden are reduced with
Delta.