African nations should use antibody tests to find out whether the slower spread and lower mortality rate of the new coronavirus on the continent is due to patchy data or a more resilient population, former British prime minister Tony Blair said on Friday.

That information would guide leaders in deciding whether to extend lockdowns or other restrictions that are damaging economies, exacerbating hunger and slowing the fight against other deadly diseases like malaria, tuberculosis and HIV/AIDS, he said.

Africa has cumulatively reported nearly 100 000 Covid-19 cases so far and just over 3 000 deaths - far fewer than in many European nations. But low rates of testing and patchy reporting of deaths mean outbreaks of the virus may be undetected in many countries.

Africa also has a much younger population than Europe - the median age is just under 20 years - and most Covid-19 fatalities are among the elderly. It's possible, though it remains unclear, that Africa will be hit less severely and measures to contain the disease could be doing more harm than good.

"The biggest risk Africa has is the cure turns out to be worse than the disease," Blair told Reuters on the day the Tony Blair Institute for Global Change, a policy think tank, launched a report about Covid-19 in Africa.

The are a wide variety of tests with varying degrees of accuracy. The two main types are antibody tests, which use blood samples to show whether you have had the disease, and more expensive molecular diagnostic tests, analysed using polymerase chain reactions (PCR), which can identify early infections.

The average antibody test currently costs between $7-$15 and a PCR test costs $12-$20, but Senegal is working on producing a cheap antibody test. Most nations are focused on PCR tests because they want to identify people who might be spreading the disease, not those who have had it.

But Blair said antibody tests - although of variable accuracy at the individual level - were invaluable to policymakers grappling with tough choices.

"Antibody tests ... shows what percentage of the population has likely been affected," Blair told Reuters.

Research by Kate Dooley at the Tony Blair Institute showed some West African countries only had lab capacity for 300 PCR tests per day while other constraints meant they were only conducting 100-200. Personnel and logistics constraints mean Nigeria, Africa's most populous country, can only carry out 2 500 tests per day despite its lab capacity for 10 000.