April 29, 2021

Impact of Vaccination on Household Transmission of SARS-COV-2 in England

[Pre-print, not peer-reviewed] Vaccinated individuals who became infected with SARS-CoV-2 had a lower rate of secondary household transmission compared to unvaccinated index individuals. Among over 550,000 residential households in the UK between January to March 2021, the overall SARS-CoV-2 secondary attack rate was 5.7% in household where the index case had received at least one dose of the Oxford-AstraZeneca and 6.3% in households where the index case had received the Pfizer-BioNTech vaccine more than 21 days before testing positive. By contrast, the overall secondary attack rate in households with unvaccinated index cases was 10%.
In a case-control analysis, contacts of index cases vaccinated with the Oxford-AstraZeneca vaccine had 38% lower odds of SARS-CoV-2 infection compared to matched contacts of unvaccinated index cases. Similarly, contacts of index cases vaccinated with the Pfizer-BioNTech vaccine had 49% lower odds of infection. [EDITORIAL NOTE: Only 7% of the vaccinated index cases had received two vaccine doses by the time of their infection, and thus the risk of secondary transmission infection may be even lower in those who have had two doses. In addition, misclassification of household transmission may also occur as all cases within 2-14 days of the index case were classified as household transmission.

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