Did Cyril overreact? Actuaries slash estimate of SA’s Covid deaths
Assa first predicted 46,000 to 88,000 deaths, but now says there are likely to be between 27,000 and 50,000
The Actuarial Society of SA (Assa) has slashed its estimates of the likely coronavirus death toll in SA in 2020, releasing a revised model that puts the probable range at between 27,000 and 50,000.
The first version of its Covid-19 model, released for comment at the end of April, predicted between 46,000 and 88,000 deaths by December.
The model is not used by the government, which relies on projections by a consortium co-ordinated by the National Institute of Communicable Diseases (NICD), but Assa’s work has added to the debate about the likely effect of Covid-19 and the appropriateness of the government’s response.
The earlier version of its model produced a limited range of scenarios and many people focused on the higher death estimate of 80,000.
“It was intended to show the sensitivity of the model to key assumptions, but people took it as the worst-case scenario,” said Assa’s Covid-19 modelling working group co-ordinator Barry Childs, who is joint CEO of Insight Actuaries.
Assa’s Covid-19 model is intended to be used by actuaries and has been updated to allow a user to be able to input a range of assumptions about key parameters, such as the extent to which the population is susceptible to the disease and the extent to which people may be asymptomatic. The earlier version did not allow for this kind of heterogeneity, said Childs.
The number of infected people in both scenarios is far higher than the number of reported cases, due to testing limitations.Actuarial Society of SA
Assa has modelled 30 scenarios to show the sensitivity of the model to changes in these kinds of assumptions.
The most likely range of deaths is captured in two scenarios. In the first, a high proportion (75%) of the population is asymptomatic and everyone is susceptible to the disease, but there is a low infection rate because there is an effective lockdown and non-medical interventions, such as social distancing. In this scenario there would be 15 million infections (most of which would be asymptomatic), 27,000 deaths and a mortality rate of 481 deaths per million population.
In scenario two, a high proportion (60%) of the population is not susceptible to the disease, a modest proportion (35%) of people are asymptomatic and there is moderate interaction between people who are infected and those who are not. Under this scenario, 10 million people would be infected and there would be 50,000 deaths, or 876 deaths per million population.
Assa emphasised that the number of infected people in both scenarios is far higher than the number of reported cases, due to testing limitations.
The model is open source and publicly available.