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South African studies suggest Omicron has higher 'asymptomatic carriage'

11 January 2022 19:55 (UTC +04:00)

Preliminary findings from two South African clinical trials suggest the Omicron coronavirus variant has a much higher rate of "asymptomatic carriage" than earlier variants, which could explain why it has spread so rapidly across the globe, APA reports citing Reuters,

The studies - one of which was carried out when Omicron infections were surging in South Africa last month and another which resampled participants around the same time - found a far greater number of people tested positive for the coronavirus but were not showing symptoms compared to previous trials.

In the Ubuntu study evaluating the efficacy of Moderna's (MRNA.O) COVID-19 vaccine in people living with HIV, 31% of 230 participants undergoing screening tested positive, with all 56 samples available for sequencing analysis verified to be Omicron.

"This is in stark contrast to the positivity rate pre-Omicron, which ranged from less than 1% to 2.4%," the researchers said in a statement.

In a subgroup of the Sisonke trial evaluating the efficacy of Johnson & Johnson's (JNJ.N) COVID-19 vaccine, the mean asymptomatic carriage rate rose to 16% during the Omicron period from 2.6% during the Beta and Delta outbreaks.

"The Sisonke study included 577 subjects previously vaccinated, ... with results suggesting a high carriage rate even in those known to be vaccinated," the researchers said.

They added that the "higher asymptomatic carriage rate is likely a major factor in the rapid and widespread dissemination of the variant, even among populations with high prior rates of coronavirus infection".