In DepthCOVID-19

Africa's pandemic puzzle: why so few cases and deaths?

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Science  14 Aug 2020:
Vol. 369, Issue 6505, pp. 756-757
DOI: 10.1126/science.369.6505.756

Science's COVID-19 reporting is supported by the Pulitzer Center and the Heising-Simons Foundation


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Children run past a mural warning about COVID-19 in Nairobi. Kenya has reported relatively few cases so far.

PHOTO: AP PHOTO/BRIAN INGANGA

Although Africa reported its millionth official COVID-19 case last week, it seems to have weathered the pandemic relatively well so far, with fewer than one confirmed case for every thousand people and just 23,000 deaths. Yet several antibody surveys suggest far more Africans have been infected with the coronavirus—a discrepancy that is puzzling scientists around the continent. “We do not have an answer,” says immunologist Sophie Uyoga of the Kenya Medical Research Institute–Wellcome Trust Research Programme.

After testing more than 3000 blood donors, Uyoga and colleagues estimated in a preprint last month that one in 20 Kenyans aged 15 to 64—or 1.6 million people—has antibodies to SARS-CoV-2, an indication of past infection. That would put Kenya on a par with Spain in mid-May, when that country had 27,000 official COVID-19 deaths. Kenya's official toll stood at 100 when the study ended. And Kenya's hospitals are not reporting huge numbers of people with COVID-19 symptoms.

Other antibody studies have yielded similarly surprising findings. From a survey of 500 asymptomatic health care workers in Blantyre, Malawi, immunologist Kondwani Jambo of the Malawi–Liverpool Wellcome Trust Clinical Research Programme and colleagues concluded that up to 12.3% of them had been exposed to the coronavirus. Based on those findings and mortality ratios for COVID-19 elsewhere, they estimated that reported number of deaths in Blantyre at the time, 17, was eight times lower than expected.

Scientists who surveyed about 10,000 people in two cities in Mozambique, Nampula and Pemba, found antibodies to SARS-CoV-2 in 3% to 10% of participants, depending on their occupation; market vendors had the highest rates, followed by health workers. Yet in Nampula, a city of approximately 750,000, a mere 300 infections had been confirmed at the time. Mozambique only has 16 confirmed COVID-19 deaths. Yap Boum of Epicentre Africa, the research and training arm of Doctors Without Borders, says many people in Cameroon have COVID-19 antibodies as well.

So what explains the huge gap between antibody data and the official toll? Part of the reason may be that Africa misses many more cases than other parts of the world because it tests far less. Kenya tests about one in every 10,000 inhabitants daily for active SARS-CoV-2 infections, one-tenth of the rate in Spain or Canada. Nigeria tests one out of every 50,000 people per day. Even many people who die from COVID-19 may not get a proper diagnosis. But in that case, you would still expect an overall rise in mortality, which Kenya has not seen, says pathologist Anne Barasa of the University of Nairobi. Uyoga cautions that the pandemic has hamstrung Kenya's mortality surveillance system, however.

Marina Pollán of the Carlos III Health Institute in Madrid, who led Spain's antibody survey, says Africa's youthfulness may protect it. Spain's median age is 45; in Kenya and Malawi, it's 20 and 18, respectively. Young people around the world are far less likely to get severely ill or die from the virus. And the population in Kenya's cities, where the pandemic first took hold, skews even younger than the country as a whole, says Thumbi Mwangi, an epidemiologist at the University of Nairobi.

Jambo is exploring the hypothesis that Africans have had more exposure to other coronaviruses that cause little more than colds in humans, which may provide some defense against COVID-19. Another possibility is that regular exposure to malaria or other infectious diseases could prime the immune system to fight new pathogens, including SARS-CoV-2, Boum adds. Barasa, on the other hand, suspects genetic factors protect the Kenyan population from severe disease.

More antibody surveys may help fill out the picture. A French-funded study will test thousands for antibodies in Guinea, Senegal, Benin, Ghana, Cameroon, and the Democratic Republic of the Congo. And 13 labs in 11 African countries are participating in a global SARS-CoV-2 antibody survey coordinated by the World Health Organization.

If tens of millions of Africans have already been infected, that raises the question of whether the continent should try for “herd immunity” without a vaccine, Boum says—the controversial idea of letting the virus run its course to allow the population to become immune, perhaps while shielding the most vulnerable. That might be preferable over control measures that cripple economies and could harm public health more in the long run.

“Maybe Africa can afford it,” given the apparent low death rate, he says. But Glenda Gray, president of the South African Medical Research Council, says it could be dangerous to base COVID-19 policies on antibody surveys. It's not at all clear whether antibodies actually confer immunity, and if so, how long it lasts, Gray notes—in which case, she asks, “What do these numbers really tell us?”

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