Endless queues in emergency departments, patients forced to try hospital after hospital to find treatment, parents sounding the alarm on social media, and the World Health Organization (WHO) expressing concern: The images arriving from northern China are an unnerving déjà vu. But this time, in addition to SARS-CoV-2, other pathogens are also at work: there's influenza A, but respiratory syncytial virus, adenoviruses, and Mycoplasma pneumoniae infections are also widespread.

Faced with this surge in infections, the Program for Monitoring Emerging Diseases (ProMED) issued an alert on Tuesday, November 21 about "a widespread epidemic of an undiagnosed respiratory disease." "It is not at all clear when this epidemic began, as it would be unusual for such a large number of children to be affected so quickly," the organization pointed out in a press release.

On November 13, the Chinese Health Commission held a press conference to report an increase in the incidence of respiratory diseases. This was not enough for the WHO, which sent out an official request for "detailed information on the increase in respiratory diseases and cases of pneumonia reported in China" on November 22. The WHO is also recommending that the Chinese population "follow measures to reduce the risk of respiratory illness," including vaccination, the wearing of masks and isolation of the sick.

While China has not made any direct announcement, the WHO released Beijing's response on Thursday evening: "The Chinese authorities have indicated that no new or unusual pathogens have been detected, nor any unusual clinical signs, including in Beijing and Liaoning, but only a general increase in the number of cases of respiratory illness due to known pathogens."

There's no "mysterious virus," as some media have put it, basing their headlines on ProMED's warning of "undiagnosed" diseases. Rather, it's a phenomenon that many countries experienced after the lifting of Covid-19 restrictions: a resurgence of other pathogens. In 2022, for example, France saw an explosion in cases of bronchiolitis, due to children's low exposure to respiratory syncytial virus for two years thanks to the application of barrier gestures.

China is the country in the world that has longest maintained an ultra-strict zero Covid policy, eventually abandoned in December 2022 under pressure from the public. "Over the past three years, thanks to the prevention and control of the [Covid] epidemic, respiratory infections have decreased, resulting in the creation of an 'immune system debt'," Li Tongzeng, head physician of the Infectious Diseases Department at Beijing's You'an Hospital, told state media.

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