For nearly three years now, China has had incredible success at keeping its number of COVID deaths relatively low. So far, the county has recorded only about 6,000 deaths among 1.4 billion people. By comparison, the U.S. has recorded more than a million deaths in a population of only 330 million.

China has accomplished this feat with what's known as a "zero COVID" policy – using strict lockdowns and community-wide testing and other measures to keep case counts close to nil.

But in the past few weeks, this strategy has begun to show signs of faltering – and some scientists think it could be crumbling.

Cases are surging to record numbers in parts of the country. On Nov. 29, China recorded an all-time daily high of more than 71,000 new cases. COVID restrictions have sparked protests and dissent in major cities at levels not seen in a decade.

Is "zero COVID" even possible with omicron? What will happen if China reopens and SARS-CoV-2 begins to transmit freely across the country? Is China prepared for a surge? Those are questions that epidemiologists and public health experts are considering. Here's a look at the key queries – and what we know so far about the possible answers.

Let's start with the basics: What does a zero-COVID policy involve? Does it really mean aiming for no cases at all?

The idea is to stop transmission of the virus inside a country. That's a tremendous challenge with a highly contagious virus like the omicron variant. Even in a country with a zero or remarkably low case count, foreign travelers may import cases and spark outbreaks from time to time. The government tries to limit both of these occurrences by severely limiting the number of people who can enter the country. And when outbreaks do occur, the government uses a combination of quarantining, contact tracing and mass testing to stamp the virus out as quickly as possible.

Since the pandemic began, about 16 countries or regions have attempted this zero-COVID approach, including Australia, New Zealand, Singapore and Taiwan.

But as SARS-CoV-2 evolved to become more transmissible, this approach has become harder and harder to carry out, says epidemiologist Jennifer Nuzzo at Brown University.

"Omicron moves through a population really quickly," she says. "It runs around the traditional public health measures that the world has used over the last two years, such as masking and quarantining."

So to maintain a zero-COVID policy, China has needed to implement extremely harsh and severe restrictions on people's movements. And they launched enormous amounts of testing on a massive scale.

For example, earlier this week, the government once again began testing millions of people in Shanghai on a daily basis. And back in the spring, the government locked down essentially all 26 million residents of the city – for a stunning two-month period. Sometimes during the lockdown, people couldn't even leave their homes to go on a walk. (Imagine New York City completely locked down for that long during the third year of the pandemic.)

So is "zero COVID" even possible with omicron? Is this approach going to work for China?

For most of the pandemic, the zero-COVID policy has worked for China, says computational biologist David Welch, at the University of Auckland. "Many countries showed that zero-COVID policy does actually work," he says. "New Zealand ran a successful zero-COVID policy for a good couple of years."

China has held case counts to remarkably low levels throughout the pandemic. The country has recorded only about 1.6 million cases since 2020, or only 0.1% of the population. And what many people don't realize is that the vast majority of those cases are asymptomatic cases detected through mass testing, says global health researcher Yanzhong Huang, at the Council on Foreign Relations. "In November, more than 90% of the 300,000 cases [in China] were asymptomatic," he says. "There are very few severe cases."

(If you're wondering why so many asymptomatic cases – it's partly because the mass testing uncovers cases that would otherwise have gone unrecorded, but otherwise ... it's a mystery.)

The problem with the zero-COVID policy, however, is that it's not sustainable year after year, both Huang and Welch say, because COVID can be found now in virtually every corner of the world. "The point of a zero-COVID policy is to use the time when you have few cases to prepare for when COVID does arrive," Welch says. The key preparation is vaccinating people to protect them against severe disease but also ensuring hospitals can handle large surges.

Over the past year and half, every other country that attempted the zero-COVID approach has abandoned it, says Jennifer Nuzzo of Brown.

Right now, it looks like the zero-COVID strategy might be starting to fail in China as well.

"Despite very aggressive measures such as high levels of mask usage, massive testing efforts and quarantining, China is still dealing with what's probably more community transmission of SARS-CoV-2 than the country is recognizing," Nuzzo says.

So is it inevitable that China will have to abandon the zero-COVID policy and stop these massive quarantines and restrictions?

"There's no sign the government is abandoning the approach," says the CFR's Yanzhong Huang. In fact, in some cities, officials have doubled down on restrictions and quarantines in the past few weeks.

"But the government may be forced to give up the approach in the coming year, I believe, if not in the coming weeks or months," he says.

Why?

"People are simply tired of the restrictions," Huang says. "Once people began to understand the nature of the virus – that it's typically mild [when you're fully vaccinated] – they started to question the zero-COVID policy" – a policy that's had huge consequences on people's lives. There have been food shortages. People have lost jobs. The country, as a whole, is cut off from the world.

If China ends these restrictions, does that mean it will likely see a massive omicron surge as other countries have?

Analysts at Bloomberg have speculated that if omicron hits in China as hard as it did in the U.S., a full reopening may lead to nearly 6 million people admitted to ICUs and more than 600,000 deaths.

One reason for this severe toll is that less than 60% of the population has had three doses of the vaccine – which is needed to give excellent protection against severe disease. Vaccination rates for elderly people in China are quite low, Huang says. On Tuesday, Chinese officials announced that 68% percent of people over age 80 have received three shots. That percentage still leaves at least 10 million at high risk for severe COVID and death.

"It's precisely this concern about the worst case scenario – with rapid increase of cases nationwide and potentially a mass die-off – that the government uses to justify zero-COVID policy," Huang says.

No country has been in this particular situation before, where they've held off the virus for so long. If China can reopen extremely slowly to limit transmission, it could possibly avoid a massive crisis.

Nonetheless, China is preparing for a big surge in severe COVID cases. The government is building more hospitals and ICU beds across the country. And it's ramping up vaccinations among the most vulnerable.

"I can't predict what will happen when the government relaxes the restrictions," Huang says. No country has been in this particular situation before, where they've held off the virus for so long – and have the tools to slow down transmission so quickly.

If China can reopen extremely slowly, to limit transmission, the country could possibly avoid a massive health crisis.