Coronavirus in South Africa: Unravelling the mystery

 South Africa’s unusually high infection rate – potentially far higher than in some European nations after their first waves – appears to have been accompanied by an uncommonly low death rate, with early data from one province suggesting that the Covid-19 mortality rate was less than half that experienced in the worst-hit countries.

Scientists warn that their preliminary figures could go up or down as more data becomes available in the coming weeks.

A total of 19,000 people will be involved in a string of nationwide surveys. Experts also note the risks involved in trying to extrapolate from one country to the rest of a continent.

But, if confirmed, these findings could have huge significance in South Africa and beyond, and might help to shed light on the reasons behind the relatively low death rate seen in many African countries, as well as helping governments to understand which communities are most at risk from the virus and how best to modify economically damaging lockdowns.

On a recent, rainy morning in Soweto, a group of health workers moved from one community to the next, taking blood tests to check for antibodies that indicate past infection by Covid-19. This type of survey is considered a far more accurate system for measuring a country’s overall infection rate than trying to extrapolate from laboratory and hospital data.

“These surveys are very important. There’s still so much that is just unknown,” said Dr Portia Mutevedzi, a senior epidemiologist at Chris Hani Baragwanath Academic Hospital in Soweto.

‘No lockdown’ in Soweto

Early results have shown a 25% infection rate in some areas, but another recent survey of participants in a vaccine trial came back with a rate of 35%, while a different group of people, living with HIV in the Western Cape hit 42%, and scientists say the real figure could be even higher in some regions, given the likelihood of false negatives as antibodies disappear over time.

The comparatively low death rates from the pandemic reported in South Africa and in many other African countries have been widely attributed by experts to demographics – with the average age on the continent roughly half that of Europe and the United States – and also to early and aggressive lockdown measures taken by many African governments, which undoubtedly helped to delay the spread of the virus and bought valuable time for countries to prepare.

Africa accounts for 17% of the global population, but approximately 3% of reported pandemic deaths. In South Africa, the official death toll stands at more than 23,000, although experts believe the true figure – as indicated by total excess deaths – is likely to be considerably higher.

 

But three senior epidemiologists involved in seroprevalence surveys in South Africa told the BBC that the emerging data could also prove, or disprove, the hypothesis that people living in high-density areas might have some extra level of immunity to Covid-19 because of greater prior exposure to other diseases.

“It’s a real scientific mystery,” said Dr Mutevedzi. “I think it’s a real possible scientific theory that [because] these crowded areas have always been prone to disease and had high infection rates so maybe that has somehow prevented them from having severe Covid-19 or from actually being infected with Covid.”

She played down the impact of government restrictions, saying that, in practice, there had been “no lockdown” in much of Soweto since people had often struggled to adhere to the rules.

“The mortality is lower here. Something has to explain it. Many people live in quite crowded settings and one theory is that pre-existing antibodies to other coronaviruses are cross-reacting,” said Prof Helen Rees, a prominent vaccine expert at Wits University.

“Well, that’s my hypothesis – that people in lower-income countries are more like to be exposed because the same thing holds true for other respiratory viruses as well as bacteria. I don’t say it’s a slam dunk, but it’s a high probability,” said Prof Shabir Madhi, who is leading a key seroprevalence survey in Gauteng province. He also oversaw South Africa’s trials for the Oxford/AstraZeneca Covid-19 vaccine.