On Wednesday, Beijing announced sweeping changes to its COVID restrictions. Those with mild and asymptomatic cases would be allowed to isolate at home, rather than be sent to government isolation facilities. Officials would no longer require PCR tests and the ubiquitous health code app to enter public venues or travel between Chinese cities. Lockdowns would be limited to individual floors or buildings, rather than entire districts.

Feng Zijian, a former deputy head of China’s Center for Disease Control and Prevention and one of Beijing’s key medical advisers, predicted on Tuesday that 60% of China might be infected with COVID in an initial surge of cases as China loosens its policies. 

By the time the disease makes its way through the population, as much as 90% of China will have been infected, he continued.

By comparison, the U.S. Centers for Disease Control and Prevention estimated in April that 60% of Americans had contracted COVID-19, up from 34% the previous December.

“It’s going to be inevitable for most of us to get infected once, regardless of how the COVID-fighting measures are adjusted,” Feng said on Tuesday.

How bad could China’s COVID wave get?

An “inevitable” surge in COVID cases would complicate China’s path out of COVID-zero. Beijing has avoided the massive outbreaks seen in just about every other country with a tough—and unpopular—policy of lockdowns, mass testing, and border controls. 

Yet experts note that China’s containment of COVID means the Chinese population lacks the immunity found in other countries, which may allow the disease to quickly spread once measures are lifted.  

China could face “millions of daily new cases for a few months, which would be orders of magnitude more than the highest number the country has witnessed thus far,” warned Goldman Sachs in a research note on Sunday, before China’s announced its new rules. 

China’s low rates of vaccination among the elderly may also make an outbreak more deadly. Only 40% of those over 80 have received a third vaccine dose.

China has pledged to vaccinate more of its elderly population, but it may not be fast enough. “If they really speed up,” China could vaccinate 70% of its over-80 population by the end of the year, yet “many people will probably die,” Alicia Garcia-Herrero, chief economist for investment bank Natixis, recently told Fortune. 

One model predicted that China could report up to 20,000 COVID deaths a day if it reopened at its current pace.

An uncontrolled outbreak might also create new COVID variants, Anthony Fauci, the White House’s chief medical adviser, warned on Wednesday. 

Why is China reopening now?

But Beijing likely couldn’t afford to put off reopening any longer, as China’s economy buckles under the weight of snap lockdowns and travel restrictions. The country’s economy is expected to miss Beijing’s 2022 GDP growth target of 5.5%: A Bloomberg poll of economists gives a consensus estimate of just 3.2% GDP growth for the year.

November’s record COVID outbreak dragged the economy down further, as officials hastily imposed lockdowns in a bid to control cases. China’s exports fell by 8.7% year on year in November, its steepest decline in over two years and far worse than analyst expectations of a 3.5% drop.

COVID disruptions are unnerving foreign companies that rely on the country for manufacturing. After a COVID outbreak in the manufacturing hub of Zhengzhou, China’s “iPhone City,” Apple is now reportedly considering using factories in other countries like India and Vietnam.

“China cannot afford to lose the jobs offered by foreign companies,” Garcia-Herrero previously told Fortune. 

Protests in Chinese cities like Beijing, Shanghai, and Guangzhou over the weekend of Nov. 26 also likely accelerated the government’s decision to ease measures.

But economists warn that even an earlier-than-expected reopening won’t spark an immediate economic rebound. A massive outbreak, even without a large death toll, would disrupt China’s economy as COVID-stricken workers stay home. 

“Lots of people will get sick, which could result in factory closures or facilities being unable to run at full capacity,” Zhang Zhiwei, chief economist for Pinpoint Asset Management, told the South China Morning Post on Monday.