Danish researchers investigate Omicron transmission in Danish households

The study included 11.937 Danish households (2.225 Omicron-infected households) and 27.874 household members in December 2021. A total of 6.397 household members tested positive 1-7 days after the primary case. The estimated secondary attack rate (SAR) was 31% and 21% in Omicron- and Deltavariant-infected households respectively.

The study found an increased transmission for unvaccinated individuals and a reduced transmission for booster-vaccinated individuals, compared to fully vaccinated individuals. Comparing households infected with the Omicron to Delta VOC, there was a significant higher transmission among fully vaccinated and booster-vaccinated indviduals [among unvaccinated individuals, OR=1,17 (95 %-CI: 0,99-1,38); among fully vaccinated individuals, OR=2,61 (95 %-CI: 2,34-2,90); among booster-vaccinated individuals, OR=3,66 (95 %-CI: 2,65-5,05)]

The results indicate that the rapid spread of the Omicron variant primarily can be ascribed to the immune evasiveness rather than an inherent increase in the basic transmissibility.
The study is published on a pre-print server (not peer-reviewed): ”SARS-CoV-2 Omicron VOC Transmission in Danish Households”