South African Study Reveals Why Omicron Variant Spreads Fast, Including In Vaccinated Individuals

COVID-19 Test Illustration. (Wikimedia Commons/Ministry of Health/East Timors)

JAKARTA - Preliminary findings from two South African clinical trials show that the Omicron variant of the coronavirus has a significantly higher rate of 'asymptomatic carriers' than previous variants, which may explain why it is spreading so rapidly around the world.

The studies, one conducted when infections of the Omicron variant spiked in South Africa last month and another that re-sampled participants around the same time, found a significantly higher number of people who tested positive for the coronavirus but were asymptomatic than in previous trials.

In the Ubuntu study evaluating the efficacy of the Moderna COVID-19 vaccine in people living with HIV, 31 percent of the 230 participants who underwent screening tested positive, with 56 samples available for sequence analysis verified as Omicron variants.

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

In the Sisonke subgroup of trials evaluating the efficacy of Johnson & Johnson's COVID-19 vaccine, the average asymptomatic carrier rate rose to 16 percent during the Omicron variant period from 2.6 percent during the Beta and Delta outbreaks.

"The Sisonke study involved 577 previously vaccinated subjects, with results showing a high degree of heritability even in those known to have been vaccinated," the researchers said.

They added, "higher rates of asymptomatic transport are likely a major factor in the rapid and widespread spread of the variant, even among populations with high rates of prior coronavirus infection".

To note, South Africa experienced a spike in COVID-19 infections from late November, around the time its scientists alerted the world to the Omicron variant.

However, new cases have since dropped back and early indications are that the wave has been characterized by less serious illness than previous ones.