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The researchers examined the transmission of Omicron subvariant BA.2 versus BA.1 in 8,541 Danish households and 17,945 household members.
The yet-to-be peer-reviewed finding, posted on the preprint repository MedRxiv, indicates that the rapid spread of BA.2 could be related to an inherent increased transmissibility of the sub-variant.
There is also evidence to support immune evasive properties of the BA.2 sub-variant, the researchers said.
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”The risk of being infected was higher in unvaccinated persons compared with vaccinated and booster-vaccinated household members in both BA.2 and BA.1 infected households,” they said.
This underlines a positive effect of vaccination towards both Omicron variants, according to the researchers.
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 sub-variant, they said.
The study also found that unvaccinated BA.2 primary cases transmit the infection to a higher degree than BA.1 primary cases, to both vaccinated and booster-vaccinated household members.
Vaccinated persons infected with BA.2, however, transmit less than vaccinated persons with BA.1, the researchers said.
”We conclude that Omicron BA.2 is inherently substantially more transmissible than BA.1, and that it also possesses immune-evasive properties that further reduce the protective effect of vaccination against infection,” the authors of the study added.
In addition to SSI, the team also included scientists from the University of Copenhagen, Statistics Denmark, and Technical University of Denmark.