U.S. COVID-19 transmission driven by ages 20-49, research finds

Sept. 22, 2020

An estimated two in three COVID-19 cases came from adults aged 20-49 according to a new report by the Imperial College London COVID-19 Response Team, the Department of Mathematics and the University of Oxford. The researchers estimate that the reproduction number (R) was only above one for adults aged 35-49, and close to one for those aged 20-34.

Only a small percentage (1.2 percent) of COVID-19 cases came from young children aged 0-9 years. The researchers say that targeting interventions to adults aged 20-49 can facilitate the safe reopening of schools and kindergartens.

The researchers looked at which age groups drove onward transmission of COVID-19 infections in the United States (until August 2020) with average percentages as follows:

0-9 years: 1.2 percent (0.8 percent -1.8 percent)      

10-19 years: 9.9 percent (9.2 percent -10.7 percent)               

20-34 years: 28.3 percent (26.9 percent -29.5 percent)         

35-49 years: 35.1 percent (34.0 percent -36.0 percent)         

50-64 years: 19.1 percent (18.6 percent -19.6 percent)             

65-79 years: 5.6 percent (3.7 percent -8.5 percent)

80+ years: 0.6 percent (0. percent -0.9 percent)

The model predicts that reopening kindergartens and elementary schools alone could lead to a substantial increase in infections and subsequent COVID-19 deaths over a three-month period in areas with ongoing community-wide transmission. With the schools opening, they estimate that the contribution to transmission (in percent) for the age group 0-9 years will increase and lead to increases across all age groups.

In most states and metropolitan areas in the United States that were evaluated, reproduction numbers were estimated to be above 1 or close to 1 for adults aged 20-49. In the United States, the report suggests that targeting interventions at adults aged 20-49 could avoid COVID-19 infections and deaths as schools reopen.

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