HONG KONG – As Covid-19 barrels through China, scientists around the world are searching for clues about an outbreak with sprawling consequences – for the health of hundreds of millions of Chinese people, the global economy and the future of the pandemic.

But in the absence of credible information from the Chinese government, it is a big scientific guessing game to determine the size and severity of the surge in the world’s most populous country.

In Hong Kong, one team of researchers pored over passenger data from five Beijing subway lines to determine the potential spread.

In Seattle, a group of modellers tried in vain to reverse-engineer an unverified government leak detailing case numbers from Chinese health officials.

In Britain, scientists are coming up with their own efficacy estimates of Chinese vaccines.

Any personal anecdote or social media report from China – scarce medicines, overrun hospitals, overflowing crematories – is possible fodder for researchers’ models.

They are all attempting to understand the same things: How quickly is the virus spreading in China? How many people are dying? Could China be the source of a new and dangerous variant?

As scientists sift through varied sources of shaky information, they are bracing for potentially catastrophic outcomes.

Barring new precautionary steps, some worst-case estimates suggest that Covid-19 could kill as many people in China in the next four months as it has Americans during the entire three-year pandemic.

Without satisfying answers, some countries are putting limits on Chinese travellers, albeit based in part on unfounded fears or political motivations.

The United States, Italy and Japan have said they will require a negative Covid-19 test for those coming from China, citing concerns that the surge in cases in China could produce new, more threatening variants.

While researchers and virus experts said the new measures would most likely do little, if anything, to blunt the spread, the policies reflect the limited visibility into the outbreak.

‘Nobody has a clue’

Scientists’ models generally point to an explosive spread and a high death rate, given how many people in China have little to no immunity to Omicron subvariants. But even their estimates are all over the place.

In the bleakest of several scenarios of what the end of China’s zero-Covid policy might mean, nearly 1 million people could die during the early months of reopening, Hong Kong researchers reported in December in a study partly funded by the Chinese Centre for Disease Control and Prevention, though the study does not provide an exact time period.

An American group estimated as many as half a million deaths by April and another 1 million by the end of 2023 if China rejects social-distancing mandates.

Airfinity, a Britain-based analytics company, this week offered an even more dire short-term forecast: 1.7 million Covid-19 deaths by the end of April.

Until December, the world seemed to have a reasonably clear understanding of what was happening with the virus in China. The ruling Communist Party proudly published low daily case numbers and deaths as a testament to its stringent zero-Covid policy. A countrywide system of lockdowns, quarantines and mass testing largely kept the virus at bay.

But in early December, the government abruptly abandoned zero-Covid, leaving the scientific community largely in the dark.

“Nobody, nobody has a clue,” said Dr Siddharth Sridhar, a clinical virologist with a focus on emerging infectious diseases.

Many more may needlessly die

Officially, China has claimed just 12 deaths from Covid-19 since Dec 1. The country has said it will only count those who die from respiratory failure directly linked to an infection, leaving out vast numbers who died because Covid-19 aggravated underlying diseases or caused heart or liver failure.

Experts say the sheer speed of the spread would suggest a much higher number of deaths.

There are also indications that officials are pressuring doctors and crematories to avoid categorising even respiratory deaths as virus related.

Several modellers have even been sceptical of leaked information from government officials on case counts, which have been used to assess the scale of China’s outbreak.

One recent estimate, making the rounds in news reports and on Chinese social media, cited data from national health officials that 250 million people had been infected in the first 20 days of December.

Some scientists said such massive figures indicated either that China has been suppressing data for months or that it is trying to make it seem like the outbreak has peaked.

“Either they know something we don’t, or they’re trying to say the worst is already over,” said Dr Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington. NYTIMES