Vaccine effectiveness against SARS-CoV-2 Delta and Omicron infection and infectiousness within households in the Netherlands between July 2021 and August 2022.

ABSTRACT

INTRODUCTION: We aimed to estimate vaccine effectiveness against infection (VE-infection) and against further transmission (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, vaccination status, calendar week and household size. RESULTS: 3,399 questionnaires concerning 4,105 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 -28% (95% CI -77%; 7%) 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 booster vaccination for those in close contact with vulnerable people to prevent transmission.