Pediatric respiratory illness outbreak in China most likely due to known pathogens

The has been a surge in pneumonia and respiratory illnesses affecting children in northern China over the past few weeks (CNN, Figure 1). This outbreak has raised alarms because Covid had emerged as a cluster of pneumonia of unknown origin cases in China in December of 2019.

Are the recent pediatric cases of unknown origin? The World Health Organization (WHO) requested more information on the infections, and in response Chinese health authorities stated that most had been caused by typical seasonal viruses, rather than any novel or unknown pathogens, These included RSV, adenovirus, influenza (flu), and coronavirus, as well as mycoplasma pneumoniae, a bacterial pathogen.  

To explain the outbreak, medical experts have pointed to the lifting of Covid lockdown restrictions in December 2022, after more than two years of some of the most stringent quarantining and social distancing efforts in the World as part of China's zero-Covid policy. This pattern is consistent with findings from other nations where pandemic restrictions have been relaxed. For example, this phenomenon was evident in the United States last autumn, when RSV cases among children spiked as fewer people practiced social distancing.

Of course, the restrictions were removed nearly one year ago in China, and so why has it taken so long for the new outbreak to occur? For one, China experienced a very large surge in Covid infections shortly after the December change in policy. The Covid cases most likely completely drowned out any spike in other infections. Second, many of the current infections are seasonal occurring primarily during cold months, and this is the first Winter since the policy change. 

A final consideration is what has been termed an "immunity debt" arising from three years of social distancing policy that depressed the infection rate for a whole host of viral and bacterial pathogens in China. As a result, there is a cohort of young children who have not been exposed to these viruses until relatively recently, and so do not possess immunity. This larger than usual group of immunologically naive children are vulnerable to an outbreak.

If China is providing accurate information to WHO, then there is most likely little to worry about. In an interview with CNN, infectious disease expert Dr. Leana Wen stated the following: 

CNN: How concerning is the spike in respiratory illnesses being reported in China?

Dr. Leana Wen: Thus far, based on what we know from WHO, I don’t think the spike in respiratory illnesses should cause global concern. What would be most worrisome to the international medical community is if a new pathogen is emerging, as it did in the form of Covid-19 in the winter of 2019. This does not appear to be the case now.

Figure 1. There has been an outbreak of respiratory illness among children in China. The culprits appear to be common seasonal viruses like RSV.