Household transmission of the SARS-CoV-2 omicron variant in New Zealand, 2022

Background: Studying the transmissibility of the SARS-CoV-2 and its driving factors is valuable due to the ongoing emergence of new variants. We examined the household transmission characteristics of the Omicron-dominant variant. Methods: The study took place in Wellington, New Zealand, from 7-February to 2-October 2022. When an individual had a confirmed case of SARS-CoV-2, all household members were instructed to take a swab every 3rd day until two consecutive negative swabs were obtained from the last person with SARS-CoV-2. Participants were monitored daily for acute respiratory symptoms until no further symptoms. Results: We enrolled 75 households with confirmed cases of SARS-CoV-2 (total enrolled individuals = 306). The median serial interval was 4 days, and the secondary attack rate (SAR) was 60.6 % (95 % confidence interval (CI) 54.1-66.7). The SAR was higher for older household contacts and lower for contacts of fully vaccinated index cases. The SAR was highest when both the index case and the contacts were unvaccinated or received only one vaccine dose (88 %). Conclusions: In this household cohort, the SARS-CoV-2 Omicron variant showed a high SAR which was modifiable by vaccination; the vaccination status of the index case and household members significantly reduced this.