Examination of 3,395 samples from blood donors earlier this year, at the tail end of the fourth wave of infections, showed that 87% of South Africans had previously been infected with the virus, while just over 97% had either had a previous infection or a vaccination or both. The study was lead by Stellenbosch University’s DST-NRF Centre of Excellence in Epidemiological Modeling and Analysis and the South African National Blood Service.

The findings demonstrate the ability of the Omicron variant, especially its BA.4 and BA.5 sublineages, to infect those who already have protection against the disease. Still, despite the proportion of positive tests nearing a record daily cases as the latest surge peaked, hospitalizations were well below previous waves and relatively few deaths were recorded. 

“The infectious pressure of the omicron variant was extraordinarily high, to have produced such a significant bump in prevalence at this relatively mature stage of the epidemic,” the researchers said. “It is hardly possible to imagine much higher prevalence values.”

With more than 100,000 deaths officially recorded, and more than three times that number if excess mortality data is used, South Africa has been the nation hardest hit by the coronavirus in Africa. Excess death data measures mortality against a historical average. 

Both the original omicron variant and the BA.4 and BA.5 sublineages were identified first in Southern Africa. The country has vaccinated half of its 40 million adults. 

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