South Africa Likely to See Fifth COVID Wave

 U.S. researchers have their eyes on South Africa as the country's COVID-19 test positivity rates rise as sharply as they did at the beginning of the first Omicron wave.

Following the original Omicron wave, there was a period of transmission of BA.2 that never took off in South Africa, though cases never dropped to pre-Omicron lows, said Jacob Lemieux, MD, PhD, an infectious diseases physician at Massachusetts General Hospital in Boston. Now, an uptick there appears to be driven by the BA.4 and BA.5 variants, he said.

"I would say that the data that's coming out of South Africa by the hour really is alarming," Lemieux said during a press briefing, pointing to graphs from South African epidemiologist and statistician Ridhwaan Suliman, PhD, that showed an "exponential rise" in test positivity rates.

BA.4 and BA.5 have risen to make up more than half of cases over the last few weeks, Lemieux noted, and "if you line up the case counts ... you start to see a rise that is reminiscent both in its numbers, its timing, and its test positivity rate of the Omicron wave, possibly taking off even faster."

In a Twitter thread today, Suliman noted that Gauteng province once again appears to be the epicenter of the outbreak, with 3,145 daily cases reported and a rolling 7-day average of more than 2,000. "Case rate up 173% week-on-week or currently doubling every 4.8 days," he tweeted, adding that the case positivity rate in the province jumped to 20.2% from 11.9% just a week prior.

Hospitalizations were up 59% week-over-week, but off a low baseline, with a total of 993 patients currently in Gauteng hospitals, he noted. "This increase is not as steep as that in infections, but needs to be monitored closely."

Deaths remain low, he said, but given the typical lag between infections and deaths, one "cannot read too much into this indicator yet," he tweeted.

While it's still too early to read into the potential severity of the current wave, he noted that early indicators "suggest a similar decoupling effect as with original Omicron wave due to high levels of population immunity. Watching closely." Population immunity in the province is estimated at over 80%, said Suliman.

Lemieux noted that BA.4 and BA.5 are circulating in the U.S., but at very low levels, and it remains to be seen whether they will outcompete other variants currently circulating. BA.2 currently accounts for 68% of sequences in the U.S., followed by BA.2.12.1, which stands at 28.7%, according to CDC's variant proportions tracker.

He said the early data "suggests that we probably will see a fifth wave in South Africa," but the extent of the wave isn't clear. "There's a lot more population level immunity, so perhaps it'll just be a wave in numbers and not in morbidity or mortality, we hope."

Lemieux added, however, that the uptick is yet more evidence against herd immunity for COVID-19: "Lots of people have quantifiable immunity, and the case numbers are not going down. That speaks to the non-sterilizing nature of the immunity. That's likely due to the overall holes, if you will, in the extent and breadth of immunity, and then also the mutations in the virus that confer immune escape."

Whether what is happening in South Africa will play out in the rest of the world is still unknown, Lemieux said.

"From a weather report standpoint, we are watching closely," he said, "but it does have a bit of a flavor of, here we go again."

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