New research: Omicron has higher asymptomatic carriage

Preliminary findings from two clinical trials in South Africa, from where Omicron was first reported, suggest that this variant of the coronavirus has a higher rate of asymptomatic “carriage” than earlier variants. Both studies found a higher rate of infection than during previous outbreaks, and a higher proportion of asymptomatic carriers.

Both studies are part of larger ones. ‘Ubuntu’, in sub-Saharan Africa, aims to evaluate the effectiveness of Moderna’s vaccine in people living with HIV. The other study is a sub-study of the ‘Sisonke’ study evaluating the effectiveness of Johnson & Johnson’s vaccine.

FINDINGS: In Ubuntu, 230 participants were initially screened in December, and 31% tested positive, all of whom were later confirmed to be Omicron. “These data are in stark contrast to Covid-19 vaccine studies conducted pre-Omicron, where the SARS-CoV-2 PCR positivity rate at the first vaccination visit ranged from <1%-2.4%,” said the study, ‘High Rate of Asymptomatic Carriage Associated with Variant Strain Omicron’, currently posted on a pre-print.

In the sub-study of Sisonke, the mean asymptomatic carriage rate among 577 participants was 16% during the Omicron period, compared to 2.6% during Beta and Delta outbreaks. The results suggest a high carriage rate even in those vaccinated, the South African Medical Research Council said in a release.

It quoted senior author Dr Lawrence Corey as saying: “Since so many people may be asymptomatic, we can’t always know who is carrying the virus, but we do know what we can do to protect ourselves and to help prevent further spread: Wear a mask; wash your hands; avoid large, indoor gatherings; and get fully vaccinated…”

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