We came across the following post on the social media platform X (formerly Twitter) by the Republican US senator Marco Rubio. Similar posts were also observed on Reddit and Telegram, including in Singapore-based channels:

The post alleges that a ‘new mysterious respiratory illness is emerging in China’, and that in response, Rubio had sent a letter to US President Joe Biden to ‘impose a travel ban on China’ until more was known about the illness.

From 1 December to 4 December, Rubio tweeted six times in support of a travel ban on China due to the ‘mystery illness’ in China.

A quick search revealed that the report of a letter to the President was genuine—Rubio had sent the letter alongside four other Republican senators. In response, a Biden administration official responded that they were ‘seeing seasonal trends’. They reported seeing nothing out of the ordinary, and saw no link between health trends in the US and the outbreak of respiratory illness in China.

From ‘Undiagnosed’ to ‘Mysterious’

There were multiple headlines about the ‘mysterious’ illness in international media that predated Rubio’s tweet. We pinpointed the origin of the allegations about the ‘mystery’ illness being a news article in the Taiwanese publication FTV News on 21 November.

Using online translation tools, the headline read, ‘Pneumonia epidemic breaks out in China! Children’s hospitals in Beijing and Liaoning are overwhelmed with sick children seeking treatment’.

Pneumonia refers to inflammation and fluid in your lungs caused by a bacterial, viral or fungal infection. While all pneumonia refers to inflammation caused by an infection in the lungs, the term itself does not describe the cause of the infection, and symptoms may be different depending on whether the root cause is a virus, bacteria or fungi.

According to a 22 November translation by ProMED, an Internet service for the International Society for Infectious Diseases to identify unusual health events, the news article said that children’s hospitals in Beijing and Liaoning, among others, were overwhelmed with sick children amid outbreaks of pneumonia.

The article quoted a Beijing citizen as saying many children were hospitalised and had fevers and pulmonary nodules (abnormal growths in the lungs that can be caused by infections). However, the citizen said the children ‘don’t cough and have no symptoms’.

The article reported that ‘parents questioned whether the authorities were covering up the epidemic’, pointing out also that the since China had dropped its zero-Covid policy at the start of 2023, ‘epidemics such as influenza, mycoplasma and bronchopneumonia have broken out from time to time’.

There was no mention of the illness being ‘mysterious’ in either the FTV article or the ProMED translation, which described the article subject as ‘undiagnosed pneumonia’.

Following ProMED’s report, the World Health Organisation (WHO) requested ‘additional epidemiologic and clinical information’ from China on 22 November regarding the ‘increase in respiratory illnesses and reported clusters of pneumonia in children’.

The WHO noted that on 13 November, Chinese authorities had ‘reported an increase in incidence of respiratory diseases in China’, attributing it to the lifting of Covid-19 restrictions and the resulting circulation of ‘known pathogens’.

These were specified as influenza, mycoplasma pneumoniae (a common bacterial infection which typically affects younger children), respiratory syncytial virus (RSV), and SARS-CoV-2 (the virus that causes COVID-19)’.

Following the WHO press statement, many international outlets such as Australia’s Sydney Morning Herald, al-Jazeera, Fortune and Forbes, reported on the undiagnosed cases of pneumonia in China, using the descriptor ‘mysterious’ or ‘mystery’ in their headlines. These media reports all addressed the likely causes of the pneumonia and the official Chinese and WHO statements.

At the time of publication of these articles, there had been no response yet to the WHO’s request for additional information from the Chinese authorities.

No Unusual Illnesses

The WHO released a new press statement on 23 November, one day after their inquiry, containing the response from the Chinese authorities. In it, the Chinese authorities advised that there had been ‘no detection of any unusual or novel pathogens or unusual clinical presentations’, and that the observed increase in respiratory illnesses was the result of known pathogens including Mycoplasma pneumoniae pneumonia since May, and RSV, adenovirus and influenza virus since October.

The statement noted that the ‘increases are earlier in the season than historically experienced’, but were not unexpected due to China’s lifting of Covid-19 restrictions only earlier this year. China also said that enhanced surveillance of outpatients and inpatients for respiratory illnesses may have contributed to the observed increase in their detection.

The WHO said that while there was ‘limited detailed information available to fully characterise the overall risk’ of the cases of respiratory illnesses in children, the trend was expected given the arrival of the winter season. It also did not recommend any specific measures for travellers to China, and advised against the application of travel or trade restrictions based on the event.

A WHO official, Maria Van Kerkhove, told Stat News in an interview that the WHO had cross-referenced China’s data with their own and found it to be reasonable. She said China’s increase in respiratory illnesses is ‘what most countries dealt with a year or two ago’ due to an ‘immunity gap’ created by the pandemic—a cohort of kids now at school-going age who had few immunological defences against viral and bacterial infections due to their reduced circulation during pandemic restrictions.

Van Kerkhove said that the information showed that the increase in illnesses was an ‘overall increased wave’ of transmission across the country, not ‘discrete clusters’ that would suggest the emergence of new pathogens.

A Wave of Infections—and Disinformation

The WHO’s investigation of the alleged clusters of undiagnosed pneumonia and their communication of their findings clearly indicates that they found no ‘mystery’ illnesses in China. However, users on social media appear to have captured the earlier headlines of the ‘mysterious’ illnesses without learning of the updated findings.

Some of these users drew links between the cases in China and other seasonal outbreaks in Europe and the US, though there being no evidence to link them and the causes likely to be the winter season and the immunity gap within each region.

Some users had also mistakenly identified ‘White Lung Syndrome’ as a description for the ‘mystery illness’. This was not a medical term, but it had been used by some health officials to describe a spike in pneumonia in children as it showed up on x-rays as a whitening of the lungs.

Anxiety over the ‘mystery’ illness seems to have been compounded by the fact that the WHO had released a similar press statement regarding an unknown pneumonia at the beginning of the Covid-19 pandemic.

Another factor may have been Taiwan issuing a travel advisory for the elderly, the very young and those with poor immunity, urging them to avoid travel to China or get vaccinations prior to travel due to the increase in respiratory illnesses there.

Ultimately, the allegations of ‘mystery’ illnesses emerging in China appear to have emerged with the earlier media headlines, which are now being perpetuated on social media and by the US senators despite new information clarifying the situation.

As such, it is false that there is a new mystery respiratory illness affecting children in China. The increase in respiratory illnesses is primarily due to a seasonal wave of known pathogens affecting a cohort of immunologically compromised children, which has disproportionately affected China in its first winter since lifting Covid-19 restrictions.