Covid-19: Omicron sub-variant BA.2 more infectious than 'original', Danish study finds

BA.2 cases account for roughly 82 per cent of cases in Denmark

By Reuters

Published: Mon 31 Jan 2022, 8:42 PM

The BA.2 sub-variant of the Omicron coronavirus variant, which has quickly taken over in Denmark, is more transmissible than the more common BA.1 and more able to infect vaccinated people, a Danish study has found.

The study, which analysed coronavirus infections in more than 8,500 Danish households between December and January, found that people infected with the BA.2 sub-variant were roughly 33 per cent more likely to infect others, compared to those infected with BA.1.

Worldwide, the “original” BA.1 sub-variant accounts for more than 98 per cent of Omicron cases, but its close cousin BA.2 has quickly become the dominant strain in Denmark, dethroning BA.1 in the second week of January.

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“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 study’s researchers said.

The study, which has not yet been peer-reviewed, was conducted by researchers at Statens Serum Institut (SSI), Copenhagen University, Statistics Denmark and Technical University of Denmark.

“If you have been exposed to Omicron BA.2 in your household, you have 39% probability of being infected within seven days. If you instead had been exposed to BA.1, the probability is 29 per cent,” lead study author Frederik Plesner told Reuters.

That suggests BA.2 is around 33 per cent more infectious than BA.1, he added.

BA.2 cases have also been registered in the United States, Britain, Sweden and Norway, but to a much lesser extent than in Denmark, where it accounts for roughly 82 per cent of cases.

The study also showed that BA.2 was relatively better than BA.1 at infecting vaccinated and booster-vaccinated people, indicating greater “immune evasive properties” of the sub-variant.

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But vaccines still played an important role, the study underlined, since both booster-vaccinated and fully vaccinated individuals were less like to get infected and transmit either sub-variants, compared to those not vaccinated.

Preliminary analysis by SSI has shown that there is no difference in the risk of hospitalisation for BA.2 compared to BA.1.

The study also confirms preliminary analysis from England, which showed BA.2 appears to have a substantial growth advantage over the BA.1 type, according to Britain’s UK Health Security Agency.