Study population and setting
Using WHO situation reports (SITREPS), authors simulated the cumulative number of reported COVID-19 cases in 45 African countries that had reported at least one case as of March 24, 2020. Using a branching model (a process that models a population in which each individual in generation X produces a random number of offsprings [i.e., secondary cases] for generation X+1), authors used reported case numbers as a proxy for the actual number of cases to forecast future epidemic trends in each country. Ten thousand epidemics were generated per country, and calendar dates by which 1,000 and 10,000 cumulative cases would occur were identified. Conditional quantiles were used to evaluate prediction accuracy (i.e., if a certain date in a country was the 0.95 quantile, then the probability of reaching the case number threshold before or at that date is 95%, whereas if the quantile for that date is 0.5, then the probability of reaching that case threshold before or at that date is 50%).
Summary of Main Findings
The model estimated that all 45 countries will reach 1,000 cumulative cases by the end of April 2020 (if not earlier), and all will reach 10,000 by mid-May 2020, only a few weeks behind the date of 1,000 cases.
In a method similar to conducting a “positive control” in a laboratory experiment, authors validated the model by applying it to countries that have already exceeded 1,000 cases. Simulated epidemics started with the first cases in each country reported to WHO SITREPS.
Authors assumed the number of reported cases was directly proportional to the number of true cases, and that there were always sufficient numbers of unreported cases to sustain transmission. Projections assumed both failed containment and no interventions to reduce transmission early in the epidemic, so these estimates are likely overestimated. Unlike other simulations in African countries, this model assumes surveillance capacity would not be overburdened, and that this would artificially slow accumulation of cases while the unreported epidemic grows unhindered.
This study adds to the growing body of projections for the impact of COVID-19 in low- and middle-income countries.