Covid-19 cases in South Africa have started to surge, largely driven by two omicron subvariants—BA.4 and BA.5—and experts say the country's next wave could be a sign of things to come in the United States, Kristina Fiore reports for MedPage Today.

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A fifth wave starts to hit South Africa

According to Jacob Lemieux, an infectious disease physician at Massachusetts General Hospital, transmission of BA.2 following the original wave of omicron cases never really took off, but now, BA.4 and BA.5 are becoming more common in South Africa, comprising more than half of all Covid-19 cases over the past few weeks.

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"[I]f 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," he said. " […] I would say that the data that's coming out of South Africa by the hour really is alarming," he added.

In a series of tweets, Ridhwaan Suliman, an epidemiologist and statistician in South Africa, noted that in the Gauteng province of the country, Covid-19 case rates are "up 173% week-on-week or currently doubling every 4.8 days," and that test positivity rates increased from 11.9% last week to 20.2% this week.

Another 3,145 #COVID19 cases reported in Gauteng 🇿🇦 today, 7-day rolling avg at 2,117 ⬆️

Case incidence = 13.4 per 100k population, up to 20% of recent peak 🏔️

Case rate up 173% week-on-week or currently doubling every 4.8 days 📈

2/n pic.twitter.com/Uc4M835Hii

— Ridhwaan Suliman (@rid1tweets) April 27, 2022

Hospitalizations are also up 59% week-to-week, Suliman said, but added that the baseline of hospitalizations was low in Gauteng. "This increase is not as steep as that in infections, but needs to be monitored closely," he said.

Hospital admissions in Gauteng 🇿🇦 have seen an increase last week, up 59% week-on-week but off a low baseline 📈

The increase is not as steep as that in infections, but needs to be monitored closely 🚑

993 patients currently in hospitals in GP, with 83 in ICU 🤲

4/n pic.twitter.com/ief2wMExnR

— Ridhwaan Suliman (@rid1tweets) April 27, 2022

Meanwhile, Covid-19 deaths remain low in Gauteng, Suliman said, but he added that, given the lag between hospitalizations and deaths, one "cannot read too much into this indicator yet."

Reported #COVID19 deaths in Gauteng 🇿🇦 remain low 🙏

Due to lag between infections and deaths, as well as reporting lag, cannot read too much into this indicator yet... However, with high levels of population immunity, >80%, hopefully more decoupling and less severe disease

5/n pic.twitter.com/Pi69QuSZbg

— Ridhwaan Suliman (@rid1tweets) April 27, 2022 

Overall, it's too early to determine how severe the potential fifth wave in South Africa could be, Suliman said, but early data suggests "a similar decoupling effect as with original Omicron wave due to high levels of population immunity," which is estimated at more than 80%, he said.

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Lemieux said early data "suggests that we probably will see a fifth wave in South Africa," but it's not yet clear what the extent of that wave will be. "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."

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Lemieux added that the wave in South Africa provides more evidence that herd immunity won't necessarily prevent more Covid-19 waves.

"Lots of people have quantifiable immunity, and the case numbers are not going down," he said. "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."

It's unclear whether the wave happening in South Africa will also occur elsewhere in the world, Lemieux said, adding that BA.4 and BA.5 are currently circulating in the United States but at low levels, and it's unclear whether they will end up becoming more prominent than the variants currently circulating. According to CDC, BA.2 accounts for 68% of all sequences in the United States, followed by BA.2.12.1 at 28.7%.

"From a weather report standpoint, we are watching closely," Lemieux said, "but it does have a bit of a flavor of, here we go again." (Fiore, MedPage Today, 4/27)