Considerable uncertainty surrounds COVID-19 - how long it will take before a vaccine is developed, the mortality rate and even how many cases there have been so far. But there is one thing of which we can be sure: social distancing works, according to mathematical modelling experts from UJ.
The team led by UJ's Prof Farai Nyabadza, an advanced researcher in mathematical epidemiology, Dr Faraimunashe Chirove, Dr Maria Visaya and Mr Williams Chukwu, have crunched the numbers and quantified the level of social distancing that can reduce pass-on rates of COVID-19 substantially. Their mathematical modelling, based on measures now in place to reduce person-to-person contact, reveals a scenario based on the impact of relaxing social distancing in which case numbers could rise to above 4000 cases by the end of the lockdown:
- Relaxing social distancing by 2% can result in a 23% rise in the number of cumulative cases
- Increasing the levels of social distancing by 2% would reduce the number of cumulative cases by about 18%
Prof Nyabadza's work is based on the reasoning that the current levels of social distancing are predicted to be inadequate especially during this infant stage of infection with exponential growth. There is a need for more aggressive and robust multi-control approaches that target reduction of the infection rate, increasing of social distancing levels, rapid detection of exposed cases and increasing the recovery of active cases need to be implemented simultaneously and optimised, says Prof Nyabadza.
But, the mathematician says, introduce COVID-19 model fitting and predictions for the cumulative infected cases for various levels of social distancing and the picture is different. The simulations show that if the optimal level of social distancing is maintained at 55%, then the number of cumulative cases will continue to grow exponentially. On this basis, Increasing the level of social distancing from 55% to 57% (ρ = 0.43), 59% (ρ = 0.41) and 61% (ρ = 0.39) would avert the cumulative cases by about 18%, 32% and 53% respectively at the end of lockdown.
Social distancing, he maintains, removes any question of people wondering whether they or a particular individual has the infection. Prof Nyabadza says: "The demand for assessment of methods of control for COVID-19 in South Africa is overwhelming. Understanding the impact of these control measures requires knowledge and expertise drawn from various scientific disciplines including mathematical modelling. The role of mathematical models' insights formed the national response to the pandemic."
Prof Nyabadza points out that social distancing has been touted as the best form of response in managing a rapid increase in the number of infected cases. "Individuals migrating into South Africa played an important role in driving the infection in South Africa, especially in the initial stages of the epidemic and the prevention of infections happening elsewhere on the globe needs special attention due to improved mobility of humans. Particular attention needs to be focused on this group of people beyond the lockdown to ensure that only COVID-19 negative cases are allowed into the country."
He says most people are following the social distancing measures and reducing their social contacts. But he says: 'We all need to go shopping sometimes. However, by following social distancing, we can all make a difference.'
Prof Nyabadza also notes that, while social distancing is currently necessary, it is also required for outbreaks of other diseases such as the Ebola Virus Disease (EVD): 'For Ebola, Educational campaigns, active case-finding and pharmaceutical interventions were among the most successful and efficient controls which helped to slow down the outbreak. As a result, the outbreak could be controlled by finding and isolating symptomatic cases. That appears not to be the situation for COVID-19, due to the wide spectrum of symptoms and the evolving scientific investigations with regards to the epidemic.
The results of social distancing may not be seen immediately, according to Prof Nyabadza, because of the time lag between transmission and individuals becoming infected and displaying symptoms. However, as his calculation demonstrates, measures implemented now can be expected to have substantial effects on future case numbers.