Effect of Vaccination on Household Transmission of SARS-CoV-2 in England
Ross Harris, Jennifer Hall, Asad Zaidi, Nick Andrews, J Kevin Dunbar, Gavin Dabrera
Abstract
Effect of Vaccination on Household Transmission of SARS-CoV-2 in EnglandTo the Editor: Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevents infection and reduces the severity of coronavirus disease 2019 (Covid-19) in vaccinated persons. 1,2We investigated whether vaccination would reduce transmission in the household setting in the context of postvaccination infection.We analyzed data from the Household Transmission Evaluation Dataset (HOSTED), which has information on all laboratory-confirmed cases of Covid-19 in England and in which data on all persons sharing the same address are linked. 3 We then linked to individual-level data on all Covid-19 vaccinations in England (see the Methods section in the Supplementary Appendix, available with the full text of this letter at NEJM.org).We compared the risk of secondary infection (defined as a positive SARS-CoV-2 test 2 to 14 days after the positive test for the index case) among unvaccinated household contacts of persons with SARS-CoV-2 infection who had received at least one dose of the ChAdOx1 nCoV-19 or BNT162b2 vaccine 21 days or more before testing positive with the risk among unvaccinated household contacts of unvaccinated persons with infection.We fitted logistic-regression models with adjustment for the age and sex of the person with the index case of Covid-19 (index patient) and the household contact, geographic region, calendar week of the index case, deprivation (a composite score of socioeconomic and other factors), and household type and size.We also considered the timing of effects among index patients who had been vaccinated at any time up to the date of the positive test.* Odds ratios were adjusted for the age and sex of the index patient and their household contact, geographic region, calendar week of the index case, and an index of multiple deprivation and household type and size.CI denotes confidence interval, and Covid-19 coronavirus disease 2019.