In Britain this week we have had scientists at Imperial College warning that levels of antibodies in the population are dropping away fast, with only 4.4 per cent of the population showing them in September – far short of the 60 to 70 per cent government scientists believe is required for the epidemic to die away thanks to herd immunity. But it is a different story in South Africa, where two of the country’s leading virologists believe that parts of the country have achieved herd immunity.
Speaking to Sky news, Marvin Hsiao of the University of Cape Town, said he couldn’t explain why infections in South Africa – which was one of the worst-affected countries in the world in the middle of the year – suddenly plummeted at the end of July. It only made sense, he said, when tests revealed much higher levels of antibodies in the population than had been believed. In Cape Town, he says, tests on pregnant women revealed that 40 per cent of them had been infected with the virus, most of whom had never developed symptoms and had no idea they were infected. Similar testing in Gauteng province, which includes Johannesburg, revealed that a third of people had been infected.
While this is still lower than many epidemiologists believe necessary to establish a level of herd immunity, others believe that it might be achieved at much lower than 60 to 70 percent.
The South African experience echoes that of the Brazilian city of Manaus, where a runaway Covid epidemic seemed to die away once 20 per cent of the population had been infected.
Ironically, Shabir Mahdi, professor of vaccinology at the University of Witwatersrand, believes that South Africa’s strict lockdown might inadvertently have spread the virus and led to the development of herd immunity. Social distancing proved impossible in many closely-packed settlements, he said, and forcing people to queue for everything promoted even more social contact than usual.
Officially, South Africa has recorded 717,000 confirmed cases of Covid-19 deaths and 19,053 deaths. Its death rate, at 320 per million people, is less than half Britain’s death rate of 671 per million – although it has a very different demographic profile.