Restoring normal population mobility to “Covid-zero regions” like China will cause some 2 million deaths in a year and the key to controlling the virus is developing vaccines that are better at preventing infection, Chinese researchers said.

China’s “zero-Covid” restrictions have come under growing scrutiny in recent weeks as it hosts the Winter Olympics in Beijing while using sweeping restrictions to try to prevent the spread of the more infectious Omicron variant.

Chinese scientists and public health specialists have reiterated the need for maintaining stringent controls, saying the risks of transmission were too high and that mass infection would put intolerable pressure on the health system.

The researchers used studies from Chile and Britain to calculate the “baseline efficacy” of current vaccines - CoronaVac in the case of Chile and the Pfizer and Oxford/AstraZeneca shots in Britain.

They estimated the baseline efficacy against symptomatic disease of the vaccines was 68.3 percent. They estimated the baseline efficacy of existing vaccines against death was 86 percent.

The efficacy estimate against infection - found to be 30 percent -is based on British data and efficacy against symptomatic disease and deaths was based on data extracted from a study on Sinovac’s CoronaVac in Chile.

But even with a global vaccination rate of 95 percent, if population mobility was restored to 2019 levels, the researchers estimated that all Covid-zero regions would see more than 234 million infections within a year, including 64 million symptomatic cases and 2 million deaths.

“The human race should continue to develop vaccines and explore new ways to improve vaccine protection against infection in order to eliminate Covid-19 at the global level,” the team of Chinese scientists said in a paper, published on Friday in the weekly bulletin of the China Center for Disease Control and Prevention (CCDC).

To reduce the incidence of Covid-19 to the levels of influenza after restoring normal mobility, the efficacy of vaccines against infection needs to be increased to 40 percent and the efficacy against symptomatic disease needs to be increased to 90 percent, they said.

They said it was more important for new vaccines to be effective against infection than against symptomatic disease or death.

“The key to controlling Covid-19 lies in the development and widespread use of vaccines that are more effective at preventing infection,” the team said.

China is the only major economy sticking with a zero-Covid policy despite warnings it could hurt growth. Others, like Singapore, Australia and New Zealand, have abandoned the strategy in favour of what policymakers call “learning to live with Covid”.

“Throughout the world, except in China and Western Australia, everyone else has moved on,” said Jaya Dantas, professor of international health at the Curtin School of Population Health in Perth, Australia, who described the Chinese paper as “very pessimistic”.

“This is basically an in-house document: it is very focused on the China scenario, and they might want to support what the government is supporting, which is a zero-Covid policy.”

China has been doubling down on its zero-Covid message and continues to seal off entire cities. The Beijing Winter Olympics are being held in a “closed-loop” bubble that some athletes have branded as excessive.

“We previously thought Covid-19 could be basically contained through vaccines but now it seems that there’s no simple method to control it except with comprehensive measures,” the CCDC’s chief epidemiologist Wu Zunyou told the Communist Party-run Global Times on Sunday.