Parts of northern China have seen a surge in children with respiratory illnesses.
The WHO requested more information from Chinese health officials, who said common bugs are the cause.
Experts do not believe this is the start of a new pandemic.
Cases of respiratory illness among children in northern China have surged in recent weeks, but it's unlikely this is the start of a new pandemic, according to the World Health Organization.
The WHO has been monitoring an increase in respiratory illness among children in northern China since mid-October. At a press conference on November 13, Chinese health authorities pinned a nationwide rise in respiratory disease, mostly in children, to the lifting of COVID-19 restrictions — which mostly ended in December 2022 — and the circulation of known pathogens such as flu, mycoplasma pneumoniae, respiratory syncytial virus (RSV), and SARS-CoV-2. The WHO said on Wednesday it's unclear if these are separate events.
Fears that this could be a new pandemic were sparked on November 21, when ProMED, an infectious disease alert system, flagged up "reported clusters of undiagnosed pneumonia in children" in parts of China and hospitals becoming overwhelmed.
However, after requesting detailed information from Chinese authorities, the WHO said that no unusual or novel pathogens had been detected.
Maria Van Kerkhove, acting director of the WHO's department of epidemic and pandemic preparedness and prevention, told STAT in an interview on Friday that the spike reflects an increased wave of cases, not discrete clusters that would be more indicative of a new virus.
"You hear 'undiagnosed.' People think, well, that means they must have ruled everything else out, and therefore it's probably new. You hear 'clusters,' which means there's some people linked in space and time. 'Children' — which is always alarming — 'with pneumonia,' which indicates a level of severity. And you hear 'China.' So I think a lot of people were immediately drawn back to the beginning of the Covid pandemic and thought: Oh God. Not again."
She gave two reasons why this outbreak is not the new COVID.
1) China is likely experiencing an immunity gap
In a conference call with the WHO on Thursday, Chinese health officials presented evidence suggesting the outbreak is partly caused by what's known as an immunity gap, STAT reported.
An immunity gap is the idea that lockdowns to prevent the spread of COVID also dramatically reduced the transmission of other common viruses and bacteria, such as flu and RSV. During this time, kids who had never been exposed to these bugs developed few immunological defenses against them, so when things went back to normal, and they were able to circulate again, more children were at risk of getting sick.
Van Kerkhove told the outlet that she backs this theory. "This is expected. This is what most countries dealt with a year or two ago," she said.
François Balloux, director of the UCL Genetics Institute, expressed the same view. "China is likely experiencing a major wave of childhood respiratory infections now as this is the first winter after their lengthy lockdown, which must have drastically reduced the circulation of respiratory bugs, and hence decreased immunity to endemic bugs," he said.
Insider health correspondent Hilary Brueck reported last year amid a spike in US children getting sick with viruses that the immunity gap or "debt" does not mean children's immune systems were damaged by lockdowns and other measures to prevent the spread of COVID, as some claimed.
2) The illnesses are not caused by a new virus
Chinese health officials said that the outbreak of respiratory illness is caused by known pathogens.
Van Kerkhove said that they provided the WHO with percentages of how many cases have been caused by influenza, rhinovirus, adenovirus, and mycoplasma pneumoniae, respectively.
She said that they had not seen patients who were not diagnosable, nor a clustering of undiagnosed pneumonias.
The health authorities also told the WHO that they had not detected any new variants or subtypes of the known pathogens. "This is not an indication of a novel pathogen," she said.
Her view is shared by other public health experts too. A group of biosecurity experts from UNSW Sydney, Australia, wrote in The Conversation on Monday: "There is no indication that the current situation in China is a new pandemic, but we should always identify and pay attention to undiagnosed pneumonia clusters. Early warning systems give us the best chance of preventing the next pandemic."
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