BA.2 is more transmissible than BA.1 but vaccinated persons are less likely to be infected and to pass on infection
A new study by scientists at the University of Copenhagen, Statistics Denmark, Technical University of Denmark and Statens Serum Institut (SSI) examines the transmission of Omicron subvariant BA.2 versus BA.1 in Danish households.
The study includes 8.541 households and 17.945 household members from 20. December to 18 January and the results indicates that the rapid spread of BA.2 could be related to an inherent increased transmissibility of the subvariant. There is also evidence to support immune evasive properties of the BA.2 subvariant.
You can read the study in pre-print here.
BA.2 has an increased transmissibility compared with BA.1
The study finds an overall secondary attack rate of 39% in BA.2 infected households compared to 29% in BA.1 infected households. The risk of being infected (susceptibility) was higher in unvaccinated persons compared with vaccinated and booster-vaccinated household members in both BA.2 and BA.1 infected households, underlining a positive effect of vaccination towards both Omicron variants.
When comparing BA.2 relative to BA.1 infected households, there was an increased risk of infection in BA.2 infected households regardless of the vaccination status of the potential secondary case, indicating an inherent increased transmissibility of the BA.2 subvariant.
In addition, comparing the risk of household members being infected in BA.2 relative to BA.1 infected households, was higher in vaccinated and booster vaccinated than in unvaccinated, which suggests immune evasive properties of the BA.2 variant.
Moreover, the study finds that unvaccinated BA.2 primary cases to a higher degree than BA.1 primary cases transmit the infection to both vaccinated and booster-vaccinated household members. Vaccinated persons infected with BA.2, however, transmits less than vaccinated persons with BA.1.
The study is available in pre-print but has not yet been peer-reviewed.