Omicron has higher ‘asymptomatic carriage’ rate than previous Covid variants, studies find



micron has a much higher rate of “asymptomatic carriage” than previous coronavirus variants, studies found.

Preliminary findings based on two clinical trials in South Africa found a far greater number of people tested positive for Omicron without symptoms compared to the delta or beta strains.

In the Ubuntu study evaluating the efficacy of Moderna’s Covid vaccine in people living with HIV, 31 per cent 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 percent to 2.4 percent,” the researchers said.

In a subgroup of the Sisonke trial evaluating the efficacy of Johnson & Johnson’s vaccine, the average asymptomatic carriage rate rose to 16 percent during the omicron period from 2.6 percent 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 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.”

South Africa experienced a surge in Covid infections from late November, around the time its scientists alerted the world to omicron.

But new cases have since fallen back and early indications are that the wave has been marked by less serious disease than earlier ones.

They compared Omicron with the original strain of Covid, as well as the Delta variant.

Around 24 hours after infection, Omicron “replicated around 70 times higher than the Delta variant and the original Sars-CoV-2 virus”.

They added: “In contrast, the Omicron variant replicated less efficiently (more than 10 times lower) in the human lung tissue than the original Sars-CoV-2 virus, which may suggest lower severity of disease.”

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