According to new data, South Africa's omicron wave may have already peaked—a development that occurred much sooner than expected. However, several health experts caution against using South Africa's experience to gauge how the United States will fare with its own omicron wave.

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South Africa's omicron wave hits a peak

South Africa's omicron wave, which has been steadily increasing over the past few weeks, may have already hit its peak, AP/ABC News reports.

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For example, Gauteng province, which is South Africa's most populous region with 16 million people and the center of the nation's omicron wave, hit a peak of 16,000 new Covid-19 cases on Dec. 12. But cases have been steadily declining since then. On Tuesday, Gauteng reported just over 3,300 new cases. South Africa is seeing a similar trend nationwide, with cases dropping from almost 27,000 last week to around 15,424 on Tuesday.

"The drop in new cases nationally combined with the sustained drop in new cases seen here in Gauteng province, which for weeks has been the center of this wave, indicates that we are past the peak," said Marta Nunes, senior researcher at the vaccines and infectious diseases analytics department at the University of Witwatersrand.

However, other experts have cautioned against assuming South Africa has passed its peak number of cases with omicron, especially since the country's positivity rate remains high at 29%.

"[I]t is way too early to suggest that we have passed the peak," said Veronica Uekermann, head of the Covid-19 response team at Steve Biko Academic Hospital in South Africa. "There are too many external factors, including the movement during the holiday season and the general behavior during this period."

Why South Africa's omicron wave might have peaked early

Given omicron's increased transmissibility, the variant was expected to spread until it infected around 90% of South Africa's population. Instead, data currently suggests that infections from omicron have stopped well before that threshold.

According to New York Magazine, some experts suggest a few different factors may have influenced why South Africa's omicron wave peaked early—or at least appears to have peaked so far.

One potential reason why South Africa's omicron wave is now in decline is because of limits to testing capacity. According to Trevor Bedford, a scientist at the Fred Hutchinson Cancer Research Center, testing capacity likely has not increased enough to keep up with the actual number of infections occurring, which means many cases are being missed.

Similarly, omicron cases may be underreported, particularly if cases are asymptomatic or mild, since many people may not want to get tested or go to the hospital. This means that South Africa's true omicron peak may still be yet to come.

"Steep epidemic curve in cities where omicron surged suggests we may be missing a lot of mild or subclinical infection, and we're measuring an epidemic as it starts to peak and not at its outset," Scott Gottlieb, a former FDA commissioner, wrote in a tweet.

Two other potential factors for the decline, according to Bedford, are the possibility that only part of South Africa's population is susceptible to omicron or that omicron's chains of transmission circled back on themselves or were limited after a certain point. Both these factors would limit the number of new people omicron could either be exposed to or infect.

What could South Africa's data mean for the U.S.?

Although data from South Africa has been used to gauge omicron's trajectory, some experts have said that South Africa's experience may not reflect what other countries, including the United States, could soon see with their own omicron waves.

"Each setting, each country is different," Nunes said. "The populations are different. The demographics of the population, the immunity is different in different countries."

According to Bedford, the omicron wave in United States is likely to be less severe than previous waves. Currently, around 80% of the U.S. population has some form of immunity against the coronavirus, whether through vaccination or prior infection. This will help blunt some of omicron's effects on hospitalization and deaths.  

On the other hand, Bedford noted that omicron's attack rate, which refers to the number of people infected by the virus, could reach 50%—meaning around 160 million Americans could be infected during the country's omicron wave. And with that many cases, several health experts have warned that omicron could quickly overwhelm hospitals, even if cases are less severe.

Overall, Bedford said that, while the United States has not reached endemicity with the coronavirus, its current experience "may be, effectively, what endemicity looks like, and we can see how bad that feels."

"If we continue to have things like omicron continuing to emerge, we can maybe expect this every year," he added. (Wallace-Wells, "Intelligencer," New York Magazine, 12/18; Meldum, AP/ABC News, 12/22)