SOUTHERN CAPE NEWS - A seroprevalence study of Sars-CoV-2 antibodies among blood donors in four provinces of South Africa indicate that actual infections may be 10 times more than the number of officially diagnosed infections.
The study was conducted by the South African National Blood Service (SANBS) in conjunction with the Western Cape Blood Service (WCBS).
The blood of healthy consenting donors in the Eastern Cape, Northern Cape, Free State and KwaZulu-Natal was under the spotlight to determine how many donors have Sars-CoV-2 antibodies, which would be an indication of previous infection with the virus.
The study found an estimated seroprevalence of 63% in the Eastern Cape, 32% in the Northern Cape, 46% in Free State and 52% in KwaZulu-Natal, according to the principal investigator and SANBS acting COO, Marion Vermeulen.
Dr Karin van den Berg, lead consultant in translational research at SANBS, said, "While this level of seroprevalence may mean that a significant amount of population-level immunity has been achieved, we know that other countries have seen large outbreaks even after such strikingly high seroprevalence was reported.
The emergence of variant strains likely contributes to this phenomenon.
"To understand the situation better, we want to analyse the role of changes in major circulating variants, changes in the spectrum of disease (what proportion of infected people are asymptomatic versus those who become seriously ill) and the natural waning of individual immunity - which is gradual rather than abrupt.
"So while we cannot draw conclusions about how ambitious a vaccination campaign would now need to be to achieve something resembling elimination of Covid-19, we at least now have a relatively robust and cost-efficient process for tracking how the epidemic unfolds over time."
Prof Alex Welte, an analytical consultant to the project, said blood donors are "pretty representative" of the general public and a balanced sample of a whole population is not difficult to produce. The samples were obtained when the country was just over the crest of the second wave.
According to Vermeulen, there was no significant difference in seroprevalence by sex or age groups, but race was a significantly important factor in all four provinces. "There is no biological reason for race itself being a factor in contracting Sars-CoV-2. The reasons why we are seeing these differences among our donors are not exactly clear and need further investigation," Welte said.
White people had the lowest infection rates in all four provinces while other races displayed higher infection rates.
The SANBS is planning to expand testing to other provinces and it is believed that the same consistent features found in these four provinces would be found in the other five provinces, according to Vermeulen.
Provincial seroprevalence estimates compared with the actual diagnosed cases of Sars-CoV-2 infection.
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