China’s massive COVID-19 outbreak probably peaked in late December, according to a preliminary analysis on the number of infections late last year and data on travel between cities. But public-health experts are frustrated by a lack of official data on the magnitude and severity of the outbreak.
For close to three years, China’s strict zero-COVID policy kept infections at bay. But since President Xi Jingping abruptly changed course and abandoned the policy in December, the Omicron variant of the coronavirus has spread largely unmitigated across the country.
Yet there are signs that the current wave of infections has already crested in many parts of China, according to Shengjie Lai, an infectious-diseases modeller at the University of Southampton, UK. In late December, Lai simulated the number of infections in different regions of China by combining information on how the variant was spreading in October and November 2022 with data on travel between cities across the country.
According to Lai’s analysis, shown to Nature but not yet published or peer reviewed, close to half of China’s cities experienced a peak in infections between 10 December and 31 December. For a further 45% of cities, the peak is predicted to occur in the first half of January.
This aligns with peak times that Lai estimated using searches for terms such as ‘fever’ and ‘COVID’ on the Internet search platform Baidu. It also fits with reports on the extent of infections in certain cities and provinces. For instance, on 21 December, the deputy director of the Chinese Center for Disease Control and Prevention (China CDC) in Beijing said during a briefing that more than 250 million people — some 18% of the population — had already been infected. And in large cities such as Beijing and Sichuan, more than 50% of residents had been infected, he said.
Meanwhile, in Henan — China’s third most populous province — an official from the province’s health commission said at a press conference that nearly 90% of Henan’s population had been infected by 6 January. The estimate was probably determined from online surveys that local health authorities are conducting around the country, according to Lai and others, because more people are being infected than are being tested.
Christopher Murray, the head of the Institute for Health Metrics and Evaluation in Seattle, Washington, is sceptical of such infection estimates, because there has been no transparency about how they were made. Modelling carried out by the institute, and published on 16 December, suggested that the country’s outbreak might not peak until as late as April.
But epidemiologist Jody McVernon at the Doherty Institute for Infection and Immunity in Melbourne, Australia, says that it makes more sense that the outbreak has already peaked, given how rapidly the Omicron variant spreads. “The idea that it would still be growing over the next few months just doesn’t make any sense,” she says.
Because the virus has already spread rapidly across China, fears that city-dwellers could unleash outbreaks in rural parts of the country during chun yun — the 40-day Lunar New Year travel period that commenced on 7 January — are probably overblown, says Lai. “The virus has already spread to the rural areas,” he says, and his modelling suggests that curbing travel would do little to alter the outbreak.
People in rural China could still be hit hard by severe illness and deaths, says Xi Chen, a health economist at Yale University in New Haven, Connecticut. Roughly 40% of China’s older population live in rural regions that lack access to larger hospitals that are better equipped to treat severe cases, he says.
Hui Jin, a public-health researcher at Southeast University in Nanjing, China, says that vaccine hesitancy is common among older people, but that vaccination rates on the Chinese mainland have increased over the past year. According to data released by the State Council’s joint prevention and control mechanism, 86% of those over the age of 60, and 66% of those older than 80, had been fully vaccinated by late November.
Death toll unknown
Epidemiologists are keen to know how many people are dying from COVID-19 in China. On 14 January, China’s National Health Commission reported that close to 60,000 people have died from COVID-19 since 8 December 2022. The figure includes 5,503 deaths from COVID-19-related respiratory failure, as well as more than 54,000 deaths in people with COVID-19 and other underlying conditions. But the number covers only people who died in hospital.
On 29 December, Zunyou Wu, chief epidemiologist at the China CDC, told a press conference that the agency was already working to assess excess mortality — a measure of how many more deaths occurred than would otherwise be expected — and has plans to publish the data.
But Murray worries that the true toll of the COVID-19 outbreak in China will be difficult to ascertain because the country’s system for recording births and deaths is incomplete.
Ariel Karlinsky, an economist at the Hebrew University in Jerusalem and a member of the World Health Organization’s technical advisory group on COVID-19 mortality assessment, says that excess-mortality data could indicate the outbreak’s death toll. But it could be another year before such data can be calculated, because deaths in 2023 will probably not be known until they are reported in China’s annual statistical yearbook in January 2024.
Although the current infection wave might be ending, McVernon notes that China is likely to face a cycle of these surges over the next year. “In having these really big, massive waves, there’s a lot of exposures all at once, and then there’s a lot of waning all at once,” she says.