The SARS-CoV-2 pandemic: Past and Future

Epidemiology | 47

implementing widespread case isolation (Wells 2020), was expected to result in a devastating impact of COVID-19 on African countries. These predictions have not materialized. There has been no COVID-19 explosion in Africa, although seroprevalence data are comparable to those from European countries like France, Italy and Spain. However, the burden and outcomes associated with COVID-19 shows substantial variations across African countries [Twahirwa 2020]. (There is no ‘one’ Africa!) In April-June 2020, the crude prevalence of anti–SARS-CoV-2 IgG among blood donors in Kenya was 5,6% (174/3098). It was highest in urban counties, Mombasa (8,0%), Nairobi (7,3%) and Kisumu (5,5%) (Uyoga 2020). Of note, Kenya had reported only 341 deaths by the end of that period. The authors conclude that the sharp contrast between the reported COVID-19 cases and deaths suggests that the disease might be attenuated in Africa. Has time come to hypothesize an “African demographic exception”? In the Democratic Republic of the Congo and Malawi, for instance, only 2-3% of the population is older than 65 years (Kalk 2020), in sharp contrast to Europe at 20,5% or Lombardy at 26%. If > 65-year-old SARS-CoV-2 infected individuals are 100 times more likely to die from COVID-19 than a 25-year-old, we should expect two different epidemics. Simply, the age pyramid might make the difference.

Natural course of a pandemic

The COVID-19 epidemic started in Wuhan, in Hubei province, China, and spread within 30 days from Hubei to the rest of mainland China, to neighboring countries (in particular, South Korea, Hong Kong and Singapore) and west to Iran, Europe and the Americas. The first huge outbreaks occurred in regions with cold winters (Wuhan, Iran, Northern Italy, the Alsace region in France). Fifty years ago, the course of the COVID-19 pandemic would have been different, with slower global spread but higher burden due to limited diagnostic and therapeutic capacities and no option of nation-wide lockdowns (see also a report of the influenza pandemics in 1957 and 1968: Honigsbaum 2020). According to one (controversial) simulation, in the absence of effective treatment and with a mortality rate of around 0,5%, without interventions COVID19 would have resulted in 7 billion infections and 40 million deaths globally during the first year (Patrick 2020). The peak in mortality (daily deaths) would have been observed approximately 3 months after the beginning of local epidemics. Another model predicted that 80% of the US population