What is the mysterious pneumonia outbreak in China?

As China experiences its first winter without strict COVID-19 restrictions since the outbreak of the pandemic three years ago, a wave of respiratory illnesses is sweeping across the country.

The unusual rise in cases has prompted the World Health Organization (WHO) to prod China for additional information on the outbreak and seek enhanced response measures. Although the cause of this trend is unclear, some health experts are attributing it to a common and temporary aftereffect of lifting lockdown restrictions, even as unanswered questions around the infections and the country of their spread have led others to draw parallels with the early days of the pandemic.

What do we know about China’s pneumonia outbreak so far?

On November 13, China’s National Health Commission reported an increase in respiratory diseases at a press conference.

On Sunday, clusters of undiagnosed pneumonia in children in northern China were reported by the Program for Monitoring Emerging Diseases (ProMED), a surveillance system that conducts global reporting of infectious disease outbreaks. It is unclear if this report overlapped with the press conference information.

According to the ProMED report, infections have proliferated in Beijing and the city of Liaoning in the country’s northeast, which are 800km (500 miles) apart.

On Wednesday, the WHO asked China to release information on the recent outbreak, including “additional epidemiologic and clinical information, as well as laboratory results from these reported clusters among children”.

Although official figures on the number of cases are not available yet, hospitals in Beijing have witnessed a surge in patients, especially in the children’s wards. “One major hospital in the city has reported that on average every day, they are seeing about 1,200 patients enter their emergency room,” Al Jazeera correspondent Katrina Yu reported from Beijing on Thursday.

Schools in Beijing are also reporting high levels of absenteeism, even dismissing entire classes for at least a week if some students are ill and warning parents to be extra cautious, Yu said.

Health officials are also worried that winter will exacerbate the spread of the infections after a warning from China’s national weather authority that, starting on Thursday, the country’s cold temperatures will plunge even further.

Why is pneumonia spreading in China?

Authorities from China’s National Health Commission attributed the rise in cases to the lifting of COVID-19 restrictions. Health experts have also agreed that this could be the reason, similar to the “lockdown exit wave” that was witnessed in countries like the United Kingdom.

China may be repaying an “immunity debt” after their lengthy lockdown, “which must have drastically reduced the circulation of respiratory bugs and hence decreased immunity to endemic bugs”, Francois Belloux, director of University College London’s Genetic Institute, said in a statement posted on X.

He added that based on current information, “there is no reason to suspect the emergence of a novel pathogen” and that Mycoplasma pneumoniae, the probable source of most cases and a bacteria that typically affects younger children, is “generally fairly harmless”.

Chinese authorities listed mycoplasma as one of the circulating pathogens along with respiratory syncytial virus (RSV) and SARS-CoV-2, the virus that causes COVID-19. The WHO has asked China for more information on the recent patterns of these microorganisms.

While the presence of a novel pathogen is a possibility until more information is made available, the outbreak could also be due to “an existing but newly mutated pathogen with modified characteristics and severity”, said Laith Abu-Raddad, professor of healthcare policy and research at Weill Cornell Medicine in Qatar.