Africa reported its millionth official Covid-19 case last week and 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 so far. 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 at the Kenya Medical Research Institute-Wellcome Trust Research Programme.After testing more than 3,000 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 was descending from its coronavirus peak and 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 in Africa 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 per cent of them had been exposed to the coronavirus.Based on those findings and mortality ratios for Covid-19 elsewhere, they estimated that the reported number of deaths in Blantyre at the time, 17, was eight times lower than expected. Scientists who surveyed about 10,000 people in the northeastern cities of Nampula and Pemba in Mozambique found antibodies to Sars-CoV-2 in three per cent to 10 per cent 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, a microbiologist and epidemiologist with Epicentre Africa, the research and training arm of Doctors Without Borders, says he found a high prevalence of Sars-CoV-2 antibodies in people from Cameroon as well, a result that remains unpublished.