Chinese Pneumonia and “Immune Debt”

Reports of a severe pneumonia in Chinese children are gathering headlines.

Early reports indicate that most cases involve school aged children being hospitalized for respiratory illnesses, including pneumonia. To date, no new viruses have been identified as the culprit.

While pneumonia is of course a potentially very serious condition, our view is that this does not seem to represent the next “pandemic.” Notably there are not widespread reports of fatalities associated with these cases. In addition many knowledgeable infectious disease experts note that an “immune debt” hypothesis makes sense –which would appear to make this more likely to be problem relatively limited to China, and some other countries that had more severe Covid restrictions than the United States.

China had some of the most severe COVID-19 lockdown policies anywhere in the world. For 2+ years, or what amounts to a large portion of the lifetime of school aged children, most Chinese have been wearing masks restricted in public gatherings etc. This can produce an effect known as “immune debt” in which the individuals who have not been exposed to the normal run-of-the-mill viruses and bacteria for an extended period do not develop the normal full
range of immune responses that normally protect against disease.1

China ended its period of severe lockdowns only in late 2022. This has been thought to create an “immune debt” particularly in children, who have not been exposed to the number and variety of “normal” respiratory viruses children would normally be exposed to, for what represents a large portion of their lifetimes. This means that large portions of Chinese citizens, particularly the young, will have to pay back this debt by being less protected against normal
respiratory viruses, now that lockdowns have been lifted.

This is the first fall season since the lifting of severe Chinese COVID restrictions. Almost all respiratory viruses are more prevalent, and more severe, in the fall and early winter. Therefore it makes medical sense that, after a period of lockdown as experienced in China, the expected “immune debt” in children would produce a rise in all types of respiratory illness among Chinese children this season.

Although information is still preliminary, and the Chinese are certainly not transparent, there are other reasons to avoid undue panic about this story. Notably it is generally true in respiratory illness that severe cases are typically clustered in the elderly as well as the young. Therefore, the fact that we are not getting reports of unusually large numbers of elderly suffering severe respiratory illness in China seems consistent with this not representing a new
and unusually dangerous respiratory virus. Rather if an “immune debt” effect is at play one would expect what seems to happening: children for whom the last two years incurred an “immune debt” by not building immunity to respiratory viruses generally, are now “paying it back” by becoming relatively more ill when exposed (for the first fall season) to the variety or “normal” respiratory illnesses.

Take Home Points:

One must be skeptical of all accounts coming from China. But at least for now we don’t see reason to panic: there are no reports of a new virus identified, or high mortality, or a corresponding wave of illness in the elderly.

Overall, the interplay of lockdowns, children and “immune debt” show that interactions between disease and public health policy are complex. School lockdowns here in the US are now understood to have caused severe, generational learning deficits in many children, hitting the disadvantaged particularly hard.2 In addition, the current Chinese experience suggests that efforts to prevent exposure to one disease now, may sometimes lead to a “debt” that has to be repaid later, sometimes in the form of more severe illness from other causes.

–Laurence M. Deutsch (12/01/23)

  2. “The pandemic has had devastating impacts on learning. What will it take to help students catch up?”