Following weeks of declining Covid-19 cases, South Africa appears to have passed its omicron wave, experts say. But while the United States is experiencing a similar rapid rise and decline in cases, several health experts say hospitals in the country are still at risk of being overwhelmed.

The omicron variant: The 'good,' 'bad,' and 'ugly' scenarios

'A flash flood more than a wave'

In December, South Africa quickly hit a peak in Covid-19 cases before seeing weeks of decline—a pattern that led some health experts to cautiously believe the country's omicron wave may already be on its way out.

In addition, a recent study published in the International Journal of Infectious Diseases found that omicron spread through the South African city of Tshwane, which researchers called the "global epicentre" of the variant, "with unprecedented speed peaking within four weeks of its commencement."

"The speed with which the omicron driven fourth wave rose, peaked and then declined has been staggering," said Fareed Abdullah, director of AIDS and tuberculosis research for the South African Medical Research Council. "Peak in four weeks and precipitous decline in another two."

"It was a flash flood more than a wave," he added.

In response to the omicron wave's peak passing, the South African government last week lifted most of its Covid-19 restrictions, including ending a late-night curfew and permitting alcohol to be once again be sold after 11 pm. However, masks are still required in public places, and public gatherings remain limited to 1,000 people indoors and 2,000 people outdoors.

Could the same pattern be seen in the U.S.?

Although countries currently struggling with their own omicron waves may look to South Africa as a potential guide for the coming weeks, some infectious disease experts have warned against using South Africa's experience to predict how others will fare.

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"Each setting, each country is different," said Marta Nunes, senior researcher at the vaccines and infectious diseases analytics department at the University of Witwatersrand. "The populations are different. The demographics of the population, the immunity is different in different countries."

According to the Washington Post, South Africa has a relatively young population in comparison with other countries, and a population that likely had "some measure of immunity," either from vaccination, prior infection, or a combination of both. It is also in the middle of summer in South Africa, a time when respiratory illnesses are less common.

In comparison, the United States has experienced less exposure overall, NPR reports, so infection could result in more severe cases. And research suggests that the overall daily number of new cases in the United States—which at 356,000 are already at an all-time high—could hit as high as 400,000 per day by mid-January, according to NPR.

However, some infectious disease experts have predicted that the United States may see a similar rapid peak and decline in cases similar to South Africa. "We'll be in for a tough January, as cases will keep going up and peak, and then fall fast," said Ali Mokdad, an epidemiologist at the University of Washington.

According to Mokdad, the proportion of hospitalized patients from omicron is likely to be lower than other waves, but with many hospitals already overwhelmed with Covid-19 cases, the United States will likely struggle more with its omicron wave than South Africa did its own. (Reuters/CNBC, 12/30/21; CBS News, 12/31/21; Frazier, Axios, 12/31/21; Cheng, Washington Post, 12/31/21; Hassan, New York Times, 12/30/21; McDaniel, NPR, 12/31/21; Choi, The Hill, 12/30/21)