Impact of vaccination on SARS-CoV-2 cases in the community: a population-based study using the UK’s COVID-19 Infection Survey
Analysis of data from the UK Covid-19 Infection Survey shows vaccination with one dose of the AstraZeneca or Pfizer Covid-19 vaccines reduced the odds of a new Covid-19 infection by 65% (95% CI 60-70%; p<0.001), with no evidence that benefits varied between the two vaccines.
Source:
Oxford University
SPS commentary:
The study found that 21 days after a single dose of either the AstraZeneca or the Pfizer vaccine the rates of all new SARS-CoV-2 infections had fallen by 65% (95% CI 60-70%), symptomatic infections by 72% (69-74%), and asymptomatic infections by 57% (64-47%) (P<0.001 for all).
Among people who had a second dose of the Pfizer vaccine, infections were 70% (62% to 77%; P<0.001) lower and symptomatic infections 90% (82% to 94%; P<0.001) lower, similar to the effects in people who had previously been infected naturally (70% and 87% reductions, respectively).
The study authors commented that the results support the decision to extend the time between the first and second dose to 12 weeks, to maximise initial vaccination coverage. They do however note that the reductions in asymptomatic infections were smaller, highlighting the potential for vaccinated individuals to get Covid-19, and for limited ongoing transmission.
A linked study compared how antibody concentrations changed after a single dose of either the AstraZeneca or Pfizer vaccine, or after two doses of the Pfizer vaccine (generally given 21-42 days apart), among 45 965 people in the survey. In those without prior Covid-19 infection, antibody responses to a single dose of the AstraZeneca or Pfizer vaccine were lower in older people, especially those aged over 60 years.