Coronavirus: South Africa may have developed degree of herd immunity against Covid-19, say scientists

South Africa may have built up a form of herd immunity to Covid-19, scientists in the country have speculated, after authorities reported an unexpected drop in cases following the first peak.

At the height of the pandemic, South Africa was ranked as the world’s fifth most-affected country, but appears to have avoided a second wave of infections as currently seen in Europe and elsewhere.

A series of studies in the provinces of Western Cape and Gauteng have shown that, in some areas, up to 40 per cent of respondents had developed coronavirus antibodies, with the majority unaware that they had ever been infected.

On the back of these findings, Shabir Mahdi, a professor of vaccinology at the University of Witwatersrand, said that he believed coronavirus had generated a degree of immunity in approximately 12 to 15 million people in South Africa.

"What has happened in SA today, the only way to explain it, the only plausible way to explain it is that some sort of herd immunity has been reached when combined with the use of non-pharmaceutical interventions... like the wearing of masks, physical distancing, ensuring ventilation when indoors and so on,” Professor Mahdi told Sky News.

After the passing of the first peak, researchers based in Cape Town began testing for traces of the virus in blood samples provided at local clinics by pregnant woman and HIV patients.

The results showed that, on average, 37 per cent of pregnant women and 42 per cent of people living with HIV tested for positive for Covid-19 antibodies.

Although clinical studies are ongoing, there is no certainty how much protection antibodies offer - or for how long.

A similar study in Gauteng province, which is dominated by the urban areas of Johannesburg and Pretoria, revealed that approximately one third of those tested had been infected with Covid-19.

Dr Marvin Hsiao, a senior lecturer and consultant virologist at the University of Cape Town, said these findings explained the sudden drop in cases after the first peak.

"Inexplicably, the numbers (of those infected with Covid-19) started dropping off at the end of July, and at the time I couldn't explain why," he said.

"But when we analysed the data it become clear, this immunity within the population level (linked to) the big surge infections is probably the main reason why we've seen the decrease of numbers of infected."

Researchers believe that South Africa’s strict lockdown, which was implemented in March, forced people into close quarters within the densely-packed townships that surround the country’s major cities, with residents also expected to queue for essentials like food and social security payments during this period.

This created “new networks for the spread of the disease,” Dr Hsiao said, and helped to inadvertently fuel a huge wave of infections.

Dr Mahdi says the failure of lockdown to suppress Covid-19 means a higher level of immunisation - however long lasting this will be - is likely to have been built up among many South Africans.

"This inadequacy in terms of adherence of the lockdown, where inadvertently we've had transmission taking place, has resulted in a high percentage in densely populated areas becoming immune,” he said.

"There might be a question in terms of the duration of immunity... based on our experience with other coronaviruses, a mild infection is probably going to (generate immunity) for two to three years but that places us in a really good position."

He added: "It is not denying that Covid is the most important cause of death this year, superseding HIV, TB and everything else but the response needs to be much more nuanced than simply believing that a highly restrictive lockdown is going to get rid of the virus.”