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Studies show Omicron variant had a much higher rate of asymptomatic carriage

The findings from two studies into Omicron are preliminary, but in line with the bigger picture about the variant’s highly transmissible nature, says South African Medical Research Council president Professor Glenda Gray. Photo: SAMRC

The findings from two studies into Omicron are preliminary, but in line with the bigger picture about the variant’s highly transmissible nature, says South African Medical Research Council president Professor Glenda Gray. Photo: SAMRC

Published Jan 12, 2022

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Cape Town - The South African Medical Research Council (SAMRC) has reported that the preliminary findings from two separate studies showed the Omicron variant had a much higher rate of asymptomatic carriage.

The SAMRC said the studies showed that for people with no signs or symptoms of Covid-19, the rate of positive infection was 31%, while another study showed 16% asymptomatic carriage.

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Previous studies using similar sampling techniques during ancestral, beta and delta variants had rates between 1% and 2.6%, which is 7 to 12 times less.

This means that more people who had contracted the Omicron variant failed to show signs or symptoms of being infected, compared to previous variants. These asymptomatic carriers likely contributed to the rapid worldwide spread of the Omicron variant.

The Ubuntu study was launched in December to evaluate the effectiveness of Moderna’s mRNA-based Covid-19 vaccine in people living with HIV, with a sample size of 230 people.

The Sisonke study evaluated the effectiveness of the single-dose Johnson and Johnson vaccine. The Sisonke sub-study evaluated the immune response and breakthrough infections in 1 200 health workers, including those living with HIV.

SAMRC president, Professor Glenda Gray, said the findings were preliminary but in line with the bigger picture about Omicron’s highly transmissible nature.

“The larger studies were designed to analyse data at the intersection of Covid-19, vaccines and people living with HIV, but they are also giving us useful information about Omicron and how its spread differs from those of previous variants of concern,” Gray said.

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Dr Nigel Garrett, head of vaccine and HIV pathogenesis research at the Centre for the Aids Programme of Research in South Africa, said the studies were initiated because sub-Saharan Africa had been hit hard by HIV and the Covid-19 pandemic.

“Ubuntu and Sisonke will provide important data on safety, dosage and effectiveness of vaccines, but they already are helping us better understand the way this virus can change and how those changes affect transmission and severity.

“It is critical that we know how Omicron and other variants spread among those who are immunocompromised, as well as those who are not,” Garrett said.

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Desmond Tutu HIV Centre director Linda-Gail Bekker added: “We further need to devise strategies for rapid detection of asymptomatic carriage, particularly in long-term care facilities and hospitals, where transmission to high-risk populations may occur.

“Our data also strongly support the need to reach global equity with primary vaccination and to develop second-generation vaccines that may be even more protective against acquisition,” Bekker said.

Omicron was first reported to the World Health Organization in mid-November, and has quickly spread to many countries around the world.

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