South Africa’s decline in cases of Covid-19 contributes to questions about infection waves

Since mid-January, confirmed Covid-19 infections in South Africa have dropped from a record nearly 22,000 a day to about 1,000, without a large-scale vaccination campaign or strict lockdown. Less than 5% of Covid-19 tests find traces of the virus, a sign that health care institutions miss fewer cases. The government has lifted most of the remaining virus restrictions for the country of 60 million people.

The cause of this steep decline in business remains a mystery. As in other countries that have experienced surprising declines in Covid-19 cases at some point – such as India, Pakistan and some parts of Brazil – epidemiologists and virologists are compiling different explanations for why the outbreak in South Africa does not follow the pattern. . elsewhere.

It ranges from important populations that achieve adequate levels of immunity to delay transmission, to people who adhere to social distance rules, such as wearing masks and voluntarily reducing contact, while deaths before the decline have increased.

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

More than a year into the pandemic, there are still many scientists who do not know how the coronavirus moves through society, often causing waves of infections whose peaks coincide with overwhelming hospitals and a large number of deaths. In the walkways, life can feel almost normal again in some places.

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

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

Virologists continue to study the coronavirus variant, known as B. 1.351, which has driven the latest wave of infections here. The strain appears to make some existing vaccines less effective and in some cases re-infected people who had recovered from a previous attack on Covid-19.

In contrast to the slump in cases experienced by many in Europe over the past summer, the current decline in infections in South Africa has not been followed by a strict government closure. At the end of the year, which overlaps with the most important summer holiday in the Southern Hemisphere, the government closed popular beaches, tightened the night bell and banned large social gatherings and the sale of alcohol. A national mask mandate has existed since April 2020.

Indoor dining, however, was limited, and many families gathered for Christmas and New Year. Most of the restrictions only come after tens of thousands of South Africans who worked in economic centers such as Johannesburg had already traveled to see family in provinces where the Covid-19 case numbers were double those set in July during the first wave. The return of workers in early January, often combined with a shared minibus taxi which is a common mode of public transport in South Africa, created perfect conditions for the spread of the virus.

The simplest explanation for the sudden drop in mid-January in cases is that parts of the population have reached a level of immunity that has made it harder for the virus to jump between different groups, said Jinal Bhiman, a chief medical officer. scientist at the NICD, said.

Only about 1.5 million South Africans, about 2.5% of the population, tested positive for Covid-19. But it is clear that the actual level of infection was much higher. Since first increasing in May, the country has recorded more than 145,000 excess deaths, of which 85 to 95% are likely due to Covid-19, according to the South African Medical Research Center. This means that about one in every 500 people in South Africa – where the median age is a decade below the US – have died of the disease over the past ten months.

South African researchers, after testing the blood of 4,588 donors for antibodies in January, estimated that more than half of the people between the ages of 15 and 69 in the two provinces hardest hit were already Covid- 19 had. However, immunity levels in other parts of the country are unlikely to be equally high.

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

In the absence of national herd immunity, scientists focus on the role of certain networks, or individuals with many social or work contacts, in managing and eventually slowing down local outbreaks. “Many sociable people are first infected and the virus moves through these networks,” said Dr. Moultrie said. When enough people in those networks become immune, the transmission can lapse.

Researchers around the world are also studying the impact of voluntary behavior change, which can anticipate and reinforce government constraints. “As rates rise, people change their behavior,” said Saad Omer, director of the Yale Institute of Global Health. Just as a small increase in social contacts can cause an exponential increase in infections, the contraction if the infections are already decreasing can further accelerate the decline.

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

Perhaps the most difficult question to answer is what is going to happen next. Will the cases go up again, perhaps driven by another coronavirus strain, like about two months after South Africa ended its first wave of infections in September? Juliet Pulliam, who runs the South African Center for Excellence in Epidemiological Modeling and Analysis, says there is no way to know.

“I do not think it is possible to predict with certainty when, or even whether there will be a third wave in South Africa,” she said.

Write to Gabriele Steinhauser by [email protected]