More than 10 percent of people with COVID-19 are infected by someone who has the SARS-CoV-2 virus but is asymptomatic.
A critical factor in containing SARS-CoV-2, the virus that causes COVID-19, is understanding how quickly the virus spreads. Findings from a new study indicate that the SARS-CoV-2 spreads quickly due to its short serial interval, often before carriers are symptomatic.
Serial interval refers to the amount of time between when a primary case (someone who is infected) develops symptoms and when a secondary case (the person they infect) develops symptoms. Some diseases, such as Ebola virus disease, have long serial intervals so containment is relatively easy despite the virulence of the virus. Other diseases, such as influenza, have short serial intervals, which contributes to their spread.
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The authors of the study reviewed 468 COVID-19 reports of disease transmission that occurred during a three-week period in mainland China, outside of Hubei Province. Each report provided information about when symptoms first appeared in both the primary and secondary cases, as well as where the transmission likely occurred.
They found that the average serial interval for SARS-CoV-2 was approximately four days and more than 12 percent of disease transmissions occurred when the primary case was asymptomatic. These findings point to the importance of limiting exposure to the virus and can inform policymakers on which interventions might be more useful.