Theories for Africa’s low Covid- 19 death rate

AS THE threat of a Covid- 19 pandemic emerged, many felt apprehension about what would happen when it reached Africa. Concerns over overstretched and underfunded health systems and the load of diseases often led to it being talked about in apocalyptic terms.

However, it has not turned out that way. On September 29, the world passed the one million reported deaths mark. The count for Africa was 35 954. Africa accounts for 17% of the global population but only 3.5% of the reported global deaths.

There has been much discussion on what accounts for this. As leads of the Covid- 19 team in the African Academy of Sciences, we have followed the events and explanations. The emerging picture is that in many African countries, the transmission has been higher but the severity and mortality much lower than predicted.

We argue that Africa’s much younger population explains a large part of the difference. Some of the remaining gaps is probably due to under- reporting but there are other plausible explanations, ranging from climatic differences, pre- existing immunity, genetic factors and behavioural differences.

The most obvious factor is population age. Across multiple countries, the risk of dying of Covid- 19 for those aged 80 years or more is around 100 times that of people in their twenties.

A recent large, multicountry study in Europe reported declines in mortality related to higher temperature and humidity. However, a review of global data, while confirming that warm and wet climates seemed to reduce the spread, indicated that the variables alone could not explain most of the variability in disease transmission.

There’s weather variability throughout Africa. Other suggestions include the possibility of pre- existing protective immune responses due either to exposure to other pathogens or to BCG vaccination, a vaccine against TB. A large analysis showed correlations between increasing BCG coverage at a young age and better outcomes of Covid- 19.

Genetic factors may also be important. A haplotype ( a group of genes) associated with increased risk of severity and present in 30% of south Asian genomes and 8% of Europeans is almost absent in Africa.

An important possibility is that public health response of African countries, prepared by experiences ( such as outbreaks or epidemics), was more effective in limiting transmission than in other parts of the world.

However, there is a possibility that herd immunity is playing a role in limiting further transmission.

There is another important possibility: the idea that viral load ( the number of virus particles transmitted to a person) is a key determinant of severity. It has been suggested that masks reduce viral load. While WHO recommends mask- wearing, uptake has been variable and has been lower in many European countries, compared with many parts of Africa.

One thing that seems clear is that the secondary effects of the pandemic will be Africa’s real challenge. These stem from the severe interruptions of social and economic activities as well as the potentially devastating effects of reduced delivery of services including vaccination, as well as malaria, TB and HIV control programmes.

Marsh is a professor of Tropical Medicine at the University of Oxford, and Alobo is a programme manager for Grand Challenges Africa at the African Academy of Sciences. This article was first published in The Conversation