Vaccine Effectiveness Against Severe Acute Respiratory Syndrome Coronavirus 2 Delta and Omicron Infection and Infectiousness Within Households in the Netherlands Between July 2021 and August 2022

Introduction. We aimed to estimate vaccine effectiveness against infection (VE-infection) and infectiousness (VE- infectiousness) in a household setting during Delta and Omicron. Knowing these effects can aid policy makers in deciding which groups to prioritize for vaccination. Methods. Participants with a positive SARS-CoV-2 test were asked about COVID-19 vaccination status and SARS-CoV-2 testing of their household members one month later. VE-infection and VE-infectiousness was estimated using GEE logistic regression adjusting for age and vaccination status, calendar week and household size. Results. 3,409 questionnaires concerning 4,123 household members were included. During the Delta-period, VE-infection of primary series was 47% (95% CI: -27%-78%) and VE-infectiousness of primary series was 70% (95% CI: 28%-87%). During the Omicron-period, VE-infection was -36% (95% CI: -88%-1%) for primary series and -30% (95% CI: -80%-6%) for booster vaccination. The VE-infectiousness was 45% (95% CI: -14%-74%) for primary series and 64% (95% CI: 31%-82%) for booster vaccination. Discussion. Our study shows that COVID-19 vaccination is effective against infection with SARS-CoV-2 Delta and against infectiousness of SARS-CoV-2 Delta and Omicron. Estimation of VE against infection with SARS-CoV-2 Omicron was limited by several factors. Our results support vaccination for those in close contact with vulnerable people to prevent transmission.