Effect of COVID-19 Vaccination on Household Transmission of SARS-CoV-2 in the Omicron Era: The Vaccine Effectiveness, Networking, and Universal Safety (VENUS) study

OBJECTIVE: To evaluate the effectiveness of vaccination on reducing household transmission of SARS-CoV-2 among common household types in Japan during the Omicron variant wave. METHODS: This retrospective study was conducted using vaccination records, COVID-19 infection data, and resident registry data from two Japanese municipalities. Households that experienced their first COVID-19 case between January and April 2022 were categorized into two groups according to the presence/absence of children aged ≤11 years. We constructed multivariable logistic regression models with generalized estimating equations to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for household transmission according to the vaccination statuses of primary cases and household contacts. RESULTS: We analyzed 7,326 households with 17,586 contacts. In all households, the OR for household transmission was <0.6 (P<0.001) when the primary case and/or contact were vaccinated. In households with children aged ≤11 years, the OR was 0.71 (P<0.001) when only the contact was vaccinated. In households with all members aged ≥12 years, the OR was <0.5 (P<0.001) when the primary case and/or contact were vaccinated. CONCLUSIONS: COVID-19 vaccination effectively reduced household transmission in Japan during the Omicron variant wave.