First-dose vaccination with the Oxford–AstraZeneca (ChAdOx1) or Pfizer–BioNTech (BNT162b2) vaccine against SARS-CoV-2 reduced the incidence of new infections with SARS-CoV-2 in the UK by 61% and 66%, respectively, a reduction that rose to 79% and 80% after administration of the second dose, according to a study published in Nature Medicine. Vaccination was most effective at reducing new infections that were symptomatic and of a greater viral burden —the abundance of the virus in the body — with no evidence to suggest differences in efficacy according to vaccine type.
The efficacy of the Oxford–AstraZeneca (ChAdOx1) and Pfizer–BioNTech (BNT162b2) vaccines against SARS-CoV-2 has been estimated in large, randomized trials of symptomatic infection with SARS-CoV-2. However, community-based studies evaluating vaccine efficacy in the real world and, more recently, against viral variants of concern — such as the more transmissible and potentially more harmful Alpha variant first detected in the UK — are needed.
Koen Pouwels and colleagues used the UK Office for National Statistics COVID-19 infection survey to assess the effectiveness of the ChAdOx1 and BNT162b2 vaccines against any new infection with SARS-CoV-2 — including the Alpha variant. This is an extensive, community-based survey of those 2 years of age or older living in private households selected at random across the UK. Between 1 December 2020 and 8 May 2021, 1,945,071 PCR results for infection with SARS-CoV-2 were collected from 383,312 participants with a median age of 55 years. The authors found that vaccination with either ChAdOx1 or BNT162b2 significantly reduced the risk of testing positive for a new infection with SARS-CoV-2 at least 21 days after administration of the first dose (61% versus 66%, respectively). They observed that the vaccines were most effective at reducing the incidence of new infections after two doses (79% versus 80%, respectively) and against infections that were symptomatic and of high viral burden. Efficacy did not differ between vaccines, or in those with long-term health conditions.
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