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Is child to adult transmission rare?

Question: The DC public schools are supposed to be reopening on Monday. Teachers have objected saying it still isn’t safe and some critics have responded that child to adult (particularly elementary school age kids) transmission of COVID is rare. Is it true that child to adult transmission is rare? 

Answer: While I would not say that child to adult transmission is rare (it does happen), I would say that accumulating evidence indicates younger children are less likely to transmit the virus as compared with adolescents and adults.  We do not yet know whether new variants impact this dynamic. Read on for more details.  

The European CDC updated its technical report on children and the role of school settings on 23 December.  It incorporates findings from several analyses, including a literature review of available scientific research from around the world published as of 18 November.  It’s a really informative read.  With regard to this question, the European CDC’s key messages are: 

  • “Younger children (preschool and primary school aged) appear to transmit SARS-CoV-2 less often than adolescents and adults (low confidence), but younger children may also have been tested for SARS-CoV-2 less frequently than other age groups, while also having fewer opportunities for social mixing during periods of school closures than adolescents. 
  • “Onward transmission by adolescents may occur as often as by adults in household and community settings, given social mixing patterns (moderate confidence).”  
  • Note: “low confidence” means that the research “provides some indication of the likely effect” whereas “moderate confidence” means that the research “provides a good indication of the likely effect.”  Ideally we’d like evidence to accumulate to the degree that we have “high confidence.”

Since the literature review concluded, a few more studies on this topic have been published.  These studies further confirm that younger kids are less likely to transmit the virus.  For example:

  • In early December, Clinical Infectious Diseases published “A meta-analysis on the role of children in SARS-CoV-2 in household transmission clusters,” which found that children are infrequently identified as the index case of household clusters (e.g. they are not often the person who likely brought infection into the household).
  • In mid-December, National Geographic published a report on a not-yet-peer-reviewed study out of Iceland led by the deCode Genetics research company.  As NatGeo reports, this 40,000-person study found that children under 15 were about half as likely as adults to be infected, and only half as likely as adults to transmit the virus to others. Almost all the coronavirus transmissions to children came from adults.”
  • Earlier this month, Pediatrics published “COVID-19 Transmission in US Child Care Programs,” which found that “exposure to child care during the early months of the US pandemic was not associated with an elevated risk for COVID-19 transmission to providers.” [note: these data were drawn in the context of the first 3 months of the pandemic with strict public health measures being practiced in child care programs, and the data are drawn primarily from settings with children <6 years of age]