MAKING SENSE OF THE NUMBERS Modelling pandemics might be an imperfect science, but it is the best that we have. UFRIEDA HO
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mperfect-important may be the apt hybrid adjective for mathematical modelling that has taken a dominant role in how the world is trying to make sense of the unknowns of the novel coronavirus, SARS-COV-2, which causes Covid-19. The strength of mathematical modelling is in tracking and projecting likely scenarios for the progression of the disease. Strong forecasting can help guide policy and decision-making to improve planning and ensure that limited resources are allocated efficiently. The downside, though, is that any modelling by equations is only as strong as the data and numbers that get crunched. Extrapolation and analysis from projections can vary widely and be misaligned to realities. Covid-19 response is high stakes territory, not just in saving lives and limiting damage to economies and livelihoods, but also in how precedents and policies are justified. It deserves deeper scrutiny.
AN ECOSYSTEM FOR INFERENCE
South Africa’s official modelling has largely been undertaken by the South African Covid-19 Modelling Consortium made up of researchers from the National Institute for Communicable Diseases (NICD) and Wits, Cape Town and Stellenbosch universities. According to the official South African coronavirus portal, in May the country relied on ‘primarily two models’: the National Covid19 Epi Model and the National Covid-19 Cost Model. “The Epi Model seeks to capture the transmission dynamics of Covid-19 at a population level over time. This takes into account the disease
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severity and the treatment pathway that patients may encounter. This feeds into the Cost Model which represents the type, number and price of ingredients to cost responses.” In May 2020, the consortium forecasted 40 000 deaths and a million infections nationwide by the end of November. By midOctober, the death toll stood at 17 863 and 693 359 recorded positive cases. The May modelling was used by the government to decide on hard lockdowns, including the still contentious bans on alcohol and cigarettes, as well as budgets for the procurement of personal protective equipment, building field hospitals and even importing the services of 217 Cuban doctors at a cost of a reported nearly half a billion rand to shore up the local emergency response. Widespread corruption has already resulted in ongoing Special Investigation Unit inquiries and the axing of Gauteng Health Minister Bandile Masuku. On a provincial level, Professor Bruce Mellado, a physicist from the Wits School of Physics and iThemba Labs, has been part of the Gauteng Advisory Council that has informed the provincial response strategy. Mellado says no model is ‘100% perfect’. He says modelling is set by parameters and is most efficient when there is accurate data and context within a strong ecosystem of epidemiologists, healthcare workers, clinicians, policymakers, data scientists and mathematicians. “Any data is good, even if it is flawed, so long as you know where the flaws are and this comes from having the input of hundreds of people from different work streams,” says Mellado.