Carrie Lam, Hong Kong’s chief executive, said in a press conference on Tuesday that the goal of the policy was to stamp out COVID in the city in accordance with Hong Kong’s “dynamic zero-COVID” policy. “We must detect early and quarantine early to cut the transmission chain,” she said.

Lam announced that every resident will be tested three times; those who test positive will be sent immediately to quarantine facilities. Those who choose not to comply could be prosecuted, she said. “We are fighting a war [against COVID]…Let’s focus on how we can ensure the 7.4 million people in Hong Kong will embrace this compulsory universal testing.”

Hong Kong is in the throes of its worst outbreak since the beginning of the pandemic, reporting a record 8,764 cases on Wednesday. Modelers at Hong Kong University predict that by the time Hong Kong’s universal testing scheme is ready, Hong Kong may be recording over 100,000 cases per day, requiring up to 300,000 isolation units.

Dr. Siddharth Sridhar, a virologist at Hong Kong University, says the program is unlikely to achieve its goal of stopping the spread of COVID-19.

“What are you going to do with the huge surge of patients? That’s going to be a major logistical challenge,” he said, explaining that Hong Kong must rapidly expand its capacity to isolate cases or institute a citywide lockdown to stop the spread.

Hong Kong’s mass testing policy is based on mainland China’s approach.

Chinese cities such as Xi’an, Tianjin, and Beijing have stopped the spread of recent Delta and Omicron waves with widespread testing, but they’ve executed those campaigns alongside harsh lockdowns. Plus, authorities implemented drastic measures when cases were still low and quarantining all positive cases was plausible. The waves in Xi’an and Tianjin, for instance, peaked at roughly 150 cases per day.

Hong Kong, on the other hand, is undertaking a mass testing program to control a runaway outbreak. “I can’t think of another example of [a testing program] like this…Even in the mainland I don’t think they’ve had an outbreak of this size,” Sridhar said of Hong Kong’s testing program.

Hong Kong’s testing campaign may be futile in stopping the virus, but it will offer scientists unparalleled insight since—unlike China’s mass testing of mostly uninfected cities—it’s expected to collect millions of simultaneous samples from a population where COVID is widespread.

For one, Hong Kong’s mass testing may provide clues about the breakdown between symptomatic and asymptomatic cases of Omicron infections. Currently, some researchers believe that asymptomatic cases may make up as much as 80% to 90% of all cases of Omicron, but studies thus far have relied on hundreds of cases to track the spread; Hong Kong’s campaign is likely to identify tens of thousands of positive cases.

“We don’t have very good data on [asymptomatic infections and] Omicron, so that’s going to be useful,” Sridhar says.

Dr. Christopher Murray, a health economist at the University of Washington, recently wrote in The Lancet that understanding the proportion of asymptomatic infections is an important indicator of Omicron’s severity. If Hong Kong can provide a better portrait of the ratio between asymptomatic and symptomatic infections, researchers and doctors may have a better understanding of how dangerous an Omicron infection is.

“Understanding the burden of Omicron depends crucially on the proportion of asymptomatic infections,” Murray wrote.

Hong Kong’s testing program may also provide some important clues about the efficaciousness of vaccines.

Hong Kong has fully vaccinated 79.2% of its population with 19.2% receiving booster shots. Hong Kong has distributed two different jabs in its campaign, one an inactivated shot from Chinese maker Sinovac and the other an mRNA vaccine from Germany’s BioNTech (distributed locally via China’s Shanghai Fosun Pharmaceutical).

Sridhar said it is clear two doses of vaccines do not stop the spread of mild Omicron cases, but the testing program could be an important indicator of how three doses of Sinovac or BioNTech protect against transmission and mild cases. The testing program “is going to provide us with some information on how three doses do against any infection, not just symptomatic, but also asymptomatic infections as well,” he said.

Hong Kong has not said how much data it will release publicly regarding the mass testing program, but the city provides daily figures on COVID cases and, until the recent outbreak overwhelmed the system, provided detailed updates on the age of each confirmed case, as well as their location and the source of their infection.

Even before Hong Kong announced the citywide testing program, researchers lauded the region’s comprehensive data collection practices for creating a “living laboratory” for understanding COVID.