9 July More on transmission by children

Thu, 07/09/2020 - 10:05

Dear colleagues,

As you know, I’m intrigued by the question of how much children contribute to transmission and therefore, I have been digging further into the literature.

  1. First there are two virological studies, confirming that children could be transmitters:
  • The study by Christian Drosten in Charité January-April looking at PCR results from over 3700 positive cases: no difference in viral load according to age. However, very limited clinical data available: e.g. how many symptomatic versus asymptomatic?  From the discussion, it is clear that Christian Drosten is from the “children may be drivers of the epidemics” school.
  • A recent study from Geneva confirms that many PCR positive nasopharyngeal samples contain cultivable virus https://wwwnc.cdc.gov/eid/article/26/10/20-2403_article    Obviously, the samples with the highest VL were more likely to contain cultivable virus, but the presence of symptoms, sex, age…were not a determining factor of “cultivability”. It has to be noted that the amount of infectious virus may have been underestimated, because the culture was not done under ideal circumstances: they mention leftovers, processing time etc.  In addition, they used “regular” Vero cells, while a more sensitive system using TMPRSS2-overexpressing Vero’s has been described.  (TMPRSS2 is the presumed major human “spike-processing” enzyme, needed for infectivity)  


  1. Then there is mounting epidemiological evidence that children are most probably not major contributors to the epidemic.  I provide two reviews and an original study, again from Geneva, suggesting that children both in household setting and in schools do not behave like “superspreaders” at all and rather infrequently transmit to both adults and other children.  But, again, despite this evidence, we have to realize that most of these studies rely on “convenience” clinical sampling and therefore is often focusing on the few symptomatic cases, who seek medical attention.  Therefore, although children may be less infectious at individual level as compared to adults, we still do not know how much the younger age groups (including adolescents), who potentially take more risks of getting infected by their lifestyle and behavior, but remain  largely asymptomatic really contribute to the spread of the virus into the older, more vulnerable age groups.    


  1. I add some studies, showing that alternative sampling (e.g. nasal or stool) could be used to avoid the more cumbersome naso- or oropharyngeal sampling in children.  Clearly there are technical opportunities to conduct larger scale epidemiological studies that could help us to get a true picture on the contribution of various age groups to the epidemic in various settings.  I repeat that it is an unmet public health need to conduct such studies.   Children and adolescents have the right on education, social contacts and freedom to move, but older, more vulnerable generations also have the right to know what risk they run by interacting with younger generations (e.g. grand children).