The study found that Gauteng had a low prevalence of Covid-19 antibodies in the sampling performed in May. File image.
The study found that Gauteng had a low prevalence of Covid-19 antibodies in the sampling performed in May. File image.

SANBS study attempts to explain Gauteng Covid-19 infection rates during third wave

By Karishma Dipa Time of article published Jul 3, 2021

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Johannesburg - Gauteng might be a congested province that is home to millions of South Africans but the SA National Blood Service (SANBS) says it is surprised at the lower rates of Covid-19 infections during previous waves.

This week, the NPO released the preliminary results of its latest study on the impact of the novel coronavirus in the country.

Medical director Dr Karin van den Berg is not surprised Gauteng is being hit hardest by the third wave of infections.

“Some of the most interesting findings of the study were the extremely high rates of antibodies in the Eastern Cape in January and the lower rates of antibodies in Gauteng and, in particular, the Western Cape in May,” she told The Saturday Star this week.

For its study, the SANBS analysed new data from a survey of its blood donors in all provinces which was conducted to determine the prevalence of antibodies against Sars-CoV-2, the virus that causes Covid-19.

Antibodies are produced in response to infection, and remain detectable, in most people, for at least a year.

The study, in partnership with the Western Cape Blood Service, the national Department of Science and Innovation, the National Research Foundation and the SA Centre of Excellence in Epidemiology Modelling and Analysis, is one of the few ways of probing the extent of Sars-CoV-2 infection at population level.

The analysis for the SANBS study was based mainly on sampling done in May, before the third wave emerged.

While Van den Berg said she was not certain about the exact reasons for the low rates of antibodies detected in Gauteng blood donors before the third wave, the province was somewhat insulated from high infection rates during the first two waves because it could afford to take some of the precautionary measures.

“This would be speculation but I suspect that, as Gauteng is the working capital of the country, it may afford the ability to social distance.”

She said the province had a low prevalence of antibodies in the sampling performed in May. That could be because the antibodies developed during the first wave have waned or because Gauteng had relatively mild first and second waves.

“This low seroprevalence (the level of a pathogen in a population, as measured in blood serum) of 35% means that two-thirds of people are naïve and therefore have no immunity, and can become infected compared to the Eastern Cape which has a seroprevelence twice has high as Gauteng (63%), meaning only a third are naïve and unprotected.”

Van den Berg said that if the same study were conducted in about six months from now in Gauteng, the results could be vastly different.

“Again, this is speculation but I would suspect, considering the terrible third wave we are currently having, the high transmissibility of the delta variant and the existing seroprevalence of 35%, that in three months we will have a seroprevalence closer to 65% in Gauteng.”

However, she warned that by the time a similar study was conducted, donor antibodies could have waned again.

“Ideally, if SANBS had sufficient funding and antibody tests were approved more efficiently through the regulatory process, this study should be performed monthly on smaller numbers to get an idea of incidence as well as waning of antibodies.”

The SANBS study also found that the small proportion of donors who were diagnosed with Covid-19 did not, at the time of their donations, have detectable levels of antibodies.

“This is a well-known fact that some people remain sero-silent, in other words, they do not develop detectable levels of antibodies.

“One hypothesis is that their innate immune system is so strong that it is sufficient to eradicate the virus from the body without requiring a humoral response.”

She said the phenomenon had been seen in many convalescent plasma trials globally.

Last year, the SANBS also worked on the Covid-19 Convalescent Plasma Trial which aimed to assist those hardest hit by the virus, including the elderly and those with comorbidities and compromised immune systems.

This trial entailed taking blood from those who have fully recovered from Covid-19 and transferring their antibodies to others who were infected.

“All we take out is this golden liquid which is plasma, the stuff that the red and white blood cells float around in, and we return all the cells back to the donor, which means that they can donate a lot more frequently because their bone marrow and organs can replenish the plasma very quickly,” former SANBS chief executive Dr Jonathan Louw told The Saturday Star in August last year.

Van den Berg said the latest study found no difference in seroprevalence with regard to age and race factors.

“We did, however, see large differences between the race groups, with the black population in all provinces and the coloured population in the Western Cape having a higher seroprevalence than the white and Asian populations.”

The Saturday Star

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