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Rapid asymptomatic transmission of COVID-19 during the incubation period demonstrating strong infectivity in a cluster of youngsters aged 16-23 years outside Wuhan and characteristics of young patients with COVID-19: a prospective contact-tracing study

Our take —

This study tracks 22 contacts of a 22-year-old male COVID-19 case who traveled from Wuhan, China to Anhui, China. Among the 15 peers the case came in contact with at a social event prior to symptom, 40% were infected from the brief encounter, with a mean incubation period among those infected of 2 days. The study shows that young asymptomatically infected people can efficiently transmit the virus through social gatherings. This study included a small sample and thus is not strong evidence for high infectivity among youth at a population-level.

Study design

Prospective Cohort

Study population and setting

Investigators followed up with 22 contacts of a 22-year-old male who was a confirmed COVID-19 case in Anhui, China from January 23 to February 20, 2020. The contacts were between the ages of 16-23 years. The study team collected data on epidemiological (i.e. exposure history, relatives, classmates, timeline of events), clinical, and laboratory factors.

Summary of Main Findings

There was a cluster of 8 contacts age 16-23 years, who were confirmed cases including the 22-year-old male index patient, his cousin, and 6 of his classmates. The index patient traveled from Wuhan on January 19, and met with his cousin and classmates on January 21. The index patient developed symptoms on January 22; the contacts had a mean incubation period of 2 days (all with mild symptoms). There were 15 classmates total at the social event. Thus, the attack rate from the gathering was 40%, with 6 classmates becoming infected after a 2-hour contact period.

Study Strengths

The investigators provide a detailed illustration of how the virus was transmitted throughout this social network of young individuals.


There were no other clusters to include to compare the findings to, making it hard to see whether or not this was an isolated incident of rapid transmission, or something more broadly representative. It is also not entirely clear if the infected contacts contracted SARS-CoV-2 from the index case, as there was no phylogenetic testing or linkage.

Value added

This is a detailed investigation including contact tracing that includes exact timing of symptom onset, which is not widely available among contact tracing reports. The results also suggest evidence of high infectivity during the asymptomatic period among young people.