The decline in the number of Covid-19 cases in South Africa adds to questions about waves of infections

As of mid-January, confirmed Covid-19 infections in South Africa have fallen from a record high of nearly 22,000 a day to about 1,000, with no large-scale vaccination campaign or strict lockdown. Traces of the virus are found in less than 5% of Covid-19 tests, a sign that health authorities are missing fewer cases. The government has lifted most of the remaining virus restrictions on the country of 60 million people.

The cause of this sharp drop in the number of cases remains somewhat of a mystery. As in other countries that have once experienced a surprising decline in Covid-19 cases – such as India, Pakistan and some parts of Brazil – epidemiologists and virologists are gathering several explanations as to why the outbreak in South Africa is not following a set pattern. elsewhere.

Those range from major populations reaching sufficient immunity levels to slow transmission, to those more adhering to social distance rules, such as wearing masks and voluntarily diminishing contacts, when deaths were ramping up before decline.

‘Anyone who professes certainty [about why infections started dropping] lies, ”said Harry Moultrie, a senior medical epidemiologist at the National Institute for Communicable Diseases or NICD in South Africa. “There is so much uncertainty in all of this.”

More than a year after the pandemic, there are still many scientists who do not know how the coronavirus moves through society and often causes waves of infections whose peaks coincide with overwhelmed hospitals and large numbers of deaths. During the troughs, life can feel almost normal in some places in the meantime.

Filling the gaps in the global understanding of the virus can have important implications for public health decisions. These include how to calibrate government interventions like lockdowns, where vaccines can best be addressed, and when a country or region has achieved herd immunity – or if that’s even possible, given the emergence of new strains of coronavirus.

A complicating factor in South Africa, as in some other countries, is that researchers do not know what the real toll of the virus is on the population. Due to limited testing capabilities and asymptomatic infections, there is no definitive data on how many people have recovered from Covid-19 and may now be immune.

Virologists continue to study the coronavirus variant, known as B. 1,351, that powered the latest wave of infections here. The strain appears to make some existing vaccines less effective and in some cases has reinfected people who had recovered from a previous attack of Covid-19.

Contrary to the downturn in cases that affected much of Europe last summer, the current decline in infections in South Africa is not the result of a strict government-imposed lockdown. At the turn of the year, which overlaps with the southern hemisphere’s major summer holidays, the government closed popular beaches, tightened curfews, and banned large social gatherings and the sale of alcohol. There has been a national mask mandate since April 2020.

However, inside limited capacity food was allowed everywhere and many families gathered for Christmas and New Year. Most of the restrictions came after tens of thousands of South Africans working in economic centers like Johannesburg had already traveled to see family in counties where the number of Covid-19 cases doubled from the records set in July, during the first wave, were achieved. The workers’ return home in early January, often piled up in shared minibus taxis that are a common means of public transport in South Africa, created perfect conditions for the virus to spread.

The simplest explanation for the sudden drop in the number of cases in mid-January is that parts of the population had reached immunity levels that made it more difficult for the virus to jump between different groups, said Jinal Bhiman, a chief medical scientist at the NICD.

Only about 1.5 million South Africans, about 2.5% of the population, have tested positive for Covid-19. But it is clear that the actual infection level was much higher. Since the number of cases started to rise in May, the country has recorded more than 145,000 additional deaths, 85% to 95% of which are likely due to Covid-19, according to the South African Medical Research Center. That means that about one in 500 people in South Africa – where the average age is ten years lower than the US – has died of the disease in the past 10 months.

South African researchers, after testing the blood of 4,858 donors for antibodies in January, estimate that in the two hardest-hit provinces, more than half of people between the ages of 15 and 69 had already had Covid-19. But immunity levels are unlikely to be equally high in other parts of the country.

Experts have also warned that blood donors are not representative of the general population, as evidenced by the recent resurgence of infections in the Brazilian city of Manaus, where an antibody test of donated blood produced similar results last year.

In the absence of national herd immunity, scientists are focusing on the role of particular networks, or individuals with many social or work contacts, in controlling and ultimately slowing down local outbreaks. “Very social people get infected first, and the virus moves through these networks,” said Dr. Moultrie. When enough people in those networks have become immune, the transmission stops.

Researchers around the world are also studying the impact of voluntary behavioral changes, which can anticipate and amplify government-imposed restrictions. “When rates go up, people change their behavior,” said Saad Omer, director of the Yale Institute for Global Health. Just as a small increase in socializing can cause an exponential rise in infections, reducing meetings when infections are already on the decline can further accelerate the decline.

“Small changes can have huge consequences,” said Dr. Omer.

Perhaps the hardest question to answer is what’s going to happen next. Will cases increase again, perhaps driven by yet another strain of coronavirus, as happened about two months after South Africa ended its first wave of infections in September? Juliet Pulliam, who heads the South African Center of Excellence in Epidemiological Modeling and Analysis, says there’s no way to know.

“I don’t think it’s possible to predict with certainty when or even if there will be a third wave in South Africa,” she said.

Write to Gabriele Steinhauser at [email protected]