Survey reveals efficacy of Pfizer and AstraZeneca vaccines against positive COVID-19 tests
pharmafile | October 18, 2021 | News story | Sales and Marketing |
Data from the Coronavirus Infection Survey (CIS), and pillars 1 and 2 of the NHS Test and Trace have measured the reduction in risk of testing positive for COVID-19 by vaccination status and vaccination types. The greatest reduction in December 2020 to May 2021 was in participants with two doses of Pfizer-BioNTech.
The study assessed vaccine effectiveness across the Alpha and Delta variants of the virus, analysing two time periods: 1 December 2020 to 16 May 2021, when the Alpha variant was dominant, and 17 May 2021 to 14 August 2021, when the Delta variant was dominant.
The primary analysis considered all new cases of positive infection, the secondary analysis considered the impact of vaccine type (Pfizer-BioNTech or Oxford-AstraZeneca) upon new cases.
During the Alpha-dominant period (December 2020 to May 2021) the greatest risk reduction was found in those who had received two vaccine doses 14 or more days previously, a risk reduction of 79%. The risk reduction was 62% in participants with one dose 21 or more days earlier. Those not vaccinated, but previously positive, had a risk reduction tested at 65%. Pfizer-BioNTech provided a risk reduction of 80%, while two doses of Oxford-AstraZeneca reduced the risk by 76%.
Pfizer and Astra-Zeneca provided similar levels of protection against symptomatic infection during the Alpha-dominant period. These symptoms were self-reported and not professionally diagnosed.
During the Delta-dominant period (17 May to 14 August 2021), the study revealed a reduced risk in testing positive by 67% for those who had two vaccine doses 14 or more days earlier. Participants with one dose 21 or more days previously had a reduction in risk of 49%. Unvaccinated participants with previous natural infection had a reduced risk of 71%. Two doses of Pfizer reduced the risk of testing positive by 73%, Astra-Zeneca by 62%. The risk reduction of two doses was higher than that of one dose. During the Delta-dominant period, both vaccines provided similar levels of protection against symptomatic infection to those with previous natural infection.