China is now facing what is likely the world's largest COVID surge of the pandemic. China's public health officials say that possibly 800 million people could be infected with the coronavirus over the next few months. And several models predict that a half million people could die, possibly more.

"Recently, the deputy director of China CDC, Xiaofeng Liang, who' s a good friend of mine, was announcing through the public media that the first COVID wave may, in fact, infect around 60% of the population," says Xi Chen, who's a global health researcher at Yale University and an expert on China's health-care system.

That means about 10% of the planet's population may become infected over the course of the next 90 days.

Epidemiologist Ben Cowling agrees with this prediction. "This surge is going to come very fast, unfortunately. That's the worst thing," says Cowling, who's at the University of Hong Kong. "If it was slower, China would have time to prepare. But this is so fast. In Beijing, there's already a load of cases and [in] other major cities because it's spreading so fast.

The fastest spread of COVID yet

Cowling says the virus is spreading faster in China than it's spread ever before anywhere during the pandemic. It also looks to be especially contagious in the Chinese population.

To estimate a virus's transmissibility, scientists often use a parameter called the reproductive number, or R number. Basically, the R number tells you on average how many people one sick person infects. So for instance, at the beginning of the COVID pandemic, in early 2020, the R number was about 2 or 3, Cowling says. At that time, each person spread the virus to 2 to 3 people on average. During the omicron surge here in the U.S. last winter, the R number had jumped up to about 10 or 11, studies have found.

Scientists at the China National Health Commission estimate the R number is currently a whopping 16 in China durng this surge. "This is a really high level of transmissibility," Cowling says. "That's why China couldn't keep their zero-COVID policy going. The virus is just too transmissible even for them."

On top of that, the virus appears to be spreading faster in China than omicron spread in surges elsewhere, Cowling adds. Last winter, cases doubled in the U.S. every three days or so. "Now in China, the doubling time is like hours," Cowling says. "Even if you manage to slow it down a bit, it's still going to be doubling very, very quickly. And so the hospitals are going to come under pressure possibly by the end of this month."

So why is the virus spreading so explosively there?

The reason is that the population has very little immunity to the virus because the vast majority of people have never been infected. Until recently, China has focused on massive quarantines, testing and travel restrictions to keep the virus mostly out of the country. So China prevented most people from getting infected with variants that came before omicron. But that means now nearly all 1.4 billion people are susceptible to an infection.

China currently has a few highly transmissible variants of omicron spreading across the country, including one called BF.7. But these variants in China aren't particularly unique, and the U.S. currently has the same ones or similar ones, including BF.7. In the U.S., however, none of the variants appear to be spreading as quickly as they are in China.

And what about vaccines? Will they stem the surge?

About 90% of the population over age 18 have been vaccinated with two shots of a Chinese vaccine. This course offers good protection against severe disease, Cowling says, but it doesn't protect against an infection. Furthermore, adults over age 60 need three shots of the vaccine to protect against severe disease, Cowling's research has found. Only about 50% of older people have received that third shot, NPR has reported. And that leaves about 11 million people still at high risk for hospitalization and death.

"There is great uncertainty about how many severe cases there will be," says Chen at Yale University. "Right now in Beijing we don't see many severe cases." However, the outbreak could look quite different outside major coastal cities like Beijing because rural areas have much poorer health-care systems.

"In China, there's such a large geographic disparity in terms of health-care infrastructure, ICU beds and medical professionals. Most of the hospitals with advanced treatment technologies are located in Beijing, Shanghai, Guangzhou, and all the big metropolitan areas."

Despite a recent effort by the government to increase ICU capacity, Chen still thinks there are way too few ICU beds in many parts of the country. "I don't quite believe the new estimate of 10 ICU beds per 100,000 people because this new number includes something they call a 'convertible.' So these are beds that are used for other treatments, such as chemotherapy and dialysis, that they are converting to an ICU bed."

Predictions about the death toll

Several models have predicted a large death toll for this initial surge, with at least a half million deaths, perhaps up to a million.

But that number, Chen says, depends a lot on two factors.

First off, people's behavior. If people at high risk continue to quarantine voluntarily, the death toll could be lower.

Second, how well the health-care system holds up under this pressure. "This is going to be a major test – and it's unprecedented," he says. "In my memory, I have never seen such a challenge to the Chinese health-care system."

No one knows for sure what's going to happen in China. But you can make some predictions based on what's happened in neighboring places faced with a similar surge. Take Hong Kong, for instance. Like China, the city had kept COVID at bay for years. But then last winter, they suffered a massive omicron surge. Over the course of only two to three months, about 3 to 4 million — or 50% of the population — caught COVID, Cowling says.

But Cowling thinks that ultimately China will still fare much better against COVID than America has.

"China has done really well to hold back the virus for three years, and ultimately, I think, the mortality rate will still be much lower than elsewhere in the world," he says, because the country has vaccinated such a high percentage of its population overall. In other words, the death toll will likely be high, given the sheer number of people infected, but it could have been much worse without the vaccinations, he explains.

"The mortality rate in China isn't going to surpass America's mortality rate [0.3%] at this point," he says. "But China has a really tough winter ahead."