To everyone’s relief, SA’s health system has largely coped with the coronavirus pandemic, sparing the nation the harrowing spectacle of overwhelmed hospitals and mortuaries as seen in northern Italy and New York.
The question is why? And for that, researchers have no easy answer.
Every indicator used to monitor the disease’s trajectory has its limitations, but together they paint the same picture. The seven-day moving averages of detected Covid-19 cases and reported deaths, the Medical Research Council’s weekly mortality reports estimating excess deaths, the test positivity rate, hospital admissions and oxygen utilisation all point to an epidemic falling steadily since peaking in June and July.
The latest indicators come in a report by the World Health Organisation surge team working with the health department that shows a 42% drop in the number of reported Covid-19 cases and a 29% drop in Covid-19 deaths in the two weeks to September 10, while the median test positivity rate fell to 9.8%, compared with 11.4% the week before, according to health minister Zweli Mkhize.
The numbers waned despite the government’s gradual lifting of lockdown restrictions, defying expectations that increased social contact would accelerate transmission, and lending weight to calls for the curfew, liquor sale controls and international travel ban to be lifted.
The consortium of modellers advising the government recently ran a scenario analysis to try teasing out the effect of possible explanations for the drop. Factors they considered included a lower than assumed population attack rate (which captures the risk of people being infected); that people changed their behaviour to reduce risk of exposure when deaths began to rise; an increased take-up of nonmedical interventions such as social-distancing and mask-wearing regardless of the rising death rate and easing lockdown restrictions; and heterogeneity in people’s transmission, with “super-spreaders” responsible for many infections.
Combination of factors
The consortium includes experts of the SA Centre for Epidemiological Modelling and Analysis at Stellenbosch University, the Modelling and Simulation Hub, Africa at the University of Cape Town (UCT), and the Health Economics and Epidemiology Research Office at Wits. It says a combination of these factors was probably at play, but without hard evidence it is difficult to pin down the most likely explanation.
UCT infectious disease specialist Graeme Meintjes thinks the biggest clue comes from a recent seroprevalence survey in the Western Cape that found 40% of pregnant women and people with HIV using public health facilities in Cape Town for routine care had Covid-19 antibodies.
The highest rates were found in Khayelitsha (46%), Klipfontein (45%) and Mitchells Plain (42%), suggesting the virus has swept through these communities leaving most people unscathed. Given the relatively modest number of recorded cases in these communities — barely more than 8,300 in Khayelitsha with a population of more than 390,000 — it is clear official figures capture only the tip of the iceberg.
Similar figures have been recorded in the most densely populated regions in Gauteng, such as Soweto and Hillbrow.
“In high-density communities where distancing is challenging, there has probably been sufficient infection and enough immunity developed to have a substantial effect on the epidemic [because the pool of susceptible people has been sufficiently depleted to break the chain of transmission]. In more affluent communities where people live more isolated lifestyles, there probably hasn’t been the same level of infection or the same level of immunity, and what is probably protecting them is ongoing preventive measures,” says Meintjes.
His view is echoed by Wits vaccinologist Shabir Mahdhi who says the downward trajectory of SA’s epidemic has been achieved in a context of widespread adoption of nonpharmaceutical interventions, such as hand hygiene, physical-distancing and mask-wearing. If people became less vigilant, SA was likely to see a resurgence in cases, he said during a recent webinar hosted by Daily Maverick.
The consortium says SA’s health system coped largely because the epidemic took off later than in many other countries and surged at different times in different areas. That enabled doctors to take advantage of improvements in patient care as evidence emerged of the benefits of the steroid dexamethasone, placing patients on their stomachs, and high-flow nasal oxygen.
The relatively young structure of the population has also helped, it says, because while age does not affect susceptibility to infection, it is a significant risk factor for severe disease and death. But scientists such as Madhi suggest the high prevalence of noncommunicable diseases such as diabetes and hypertension may well have offset these age gains.
Scientists say it is also possible that widespread mask usage helped reduce disease severity in many infected people by their exposure to the virus. Another possible explanation for the low mortality rate despite the high prevalence is that prior exposure to other less deadly coronaviruses — such as those that cause the common cold — provide a degree of protection, says Meintjes.
Despite the waning epidemic, large parts of the population remain susceptible, he says. “It would be wrong to think we can drop our guard. Many people are still vulnerable.”
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