Reports of increased respiratory disease among children in China have put disease watchers elsewhere on alert, triggering anxiety that the outbreak — if it is indeed one outbreak — holds uncomfortable echoes of the start of the Covid-19 pandemic.
But at present, a number of experts say the activity has a likely explanation: China’s population, especially its young children, probably developed significant immunological susceptibility to a range of respiratory pathogens during the years of China’s zero Covid policy. China only lifted that diktat — and eased the draconian restrictions that made it work — in late 2022.
“This does not have any hallmarks of a new and emerging pathogen challenge,” Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, told STAT. Osterholm said the question of what’s going on in China could be quickly answered if the country provides epidemiological information — data on who is being infected — and the results of lab tests.
The World Health Organization, which was pilloried at the start of the Covid pandemic due to a perception that it should have taken a harder line with less-than-forthcoming Chinese authorities, has formally requested exactly that information.
In a statement issued Wednesday, the Geneva-based global health agency said it asked for lab results as well as surveillance data on recent transmission trends of respiratory pathogens including influenza, SARS-CoV-2, respiratory syncytial virus or RSV, and mycoplasma pneumoniae, a bacterium that is one of myriad causes of pneumonia. Reports suggest the latter is responsible for at least some of the illnesses reported in China.
The WHO said it was also seeking information from medical professionals and scientists in China through its technical partnerships and scientific networks.
The statement noted that northern China — one of the regions said to be experiencing a surge in respiratory illnesses among children — has seen higher influenza-like activity since mid-October compared to the previous three years at that time. What the statement didn’t say: During the previous three Octobers, China’s zero Covid policy was still in effect, so respiratory illness levels were likely at record lows.
This same pattern — limited transmission of respiratory pathogens during the early days of the pandemic, followed by a resurgence of high levels of influenza-like illness activity when Covid restrictions were lifted — has occurred elsewhere.
Osterholm said this could easily explain what is being seen in China now. The country was so successful in stopping the spread of respiratory pathogens that young children — especially those born since the start of the pandemic — would not be armed with the normal array of antibodies that kids typically acquire in childhood, when they experience a seemingly endless succession of colds and flu-like illnesses.
“There, immunologically, kids under age 4 are really quite naive to most of these viruses,” he said.
Ben Cowling, chair of epidemiology at Hong Kong University’s School of Public Health, told STAT recently that influenza activity in Hong Kong only resumed post-pandemic in the spring of 2023. While North America experienced no flu season during the winter of 2020-21, there was a mild flu season in 2021-22, followed by an active and abnormally early flu season in 2022-23.
Cowling said Hong Kong experienced a surge of flu cases last month, at a time when influenza transmission is not normally high. He is not currently alarmed by the respiratory activity in China. “There’s been a winter surge for more than a month already,” Cowling said in an email. “Doesn’t seem to be anything panic-worthy.”
Other experts have noted that the fact that the illnesses appear to be occurring mostly in children points away from the notion that a new pathogen might be circulating. (There have also been some cases reported among teachers.) Were there to be a new bug, both children and adults would lack immunity to it, leading to cases at all ages.
“Overall, this does not sound to me like an epidemic due to a novel virus. If it was, I would expect to see many more infections in adults,” Paul Hunter, a professor of medicine at the United Kingdom’s University of East Anglia, said in a statement circulated by the U.K.’s Science Media Center.
Francois Balloux, director of the University College London’s Genetics Institute, also pointed to the possibility that higher-than-normal activity caused by a known respiratory bug or bugs could be due to the accumulation of immunological susceptibility during the zero Covid era.
“Other countries, including the U.K., experienced big waves of respiratory infections and hospitalizations in kids during their first winter after pandemic restrictions had been lifted,” Balloux said in the Science Media Center statement. “Since China experienced a far longer and harsher lockdown than essentially any other country on earth, it was anticipated that those ‘lockdown exit’ waves could be substantial in China.”