Half of COVID-19 Transmission Is From Asymptomatic Individuals
Approximately 59% of all transmission of COVID-19 is from asymptomatic individuals, according to new data. Of these individuals, 35% were presymptomatic and 24% never experienced symptoms.
"In this decision analytical model of multiple scenarios of proportions of asymptomatic individuals with COVID-19 and infectious periods, transmission from asymptomatic individuals was estimated to account for more than half of all transmissions,” the researchers wrote.
At the beginning of the SARS-COV-2 pandemic, early studies from China determined the median day of peak infectiousness was day 5, which was used as the baseline to generate data for this study. When researchers adjusted the day of peak infectiousness, the transmission rates changed as well. When the peak infectiousness was shifted by 1 day sooner (to day 4), presymptomatic transmission increased to 43%, and all asymptomatic transmission increased to 67%. When the peak was shifted 1 day later (to day 6), presymptomatic transmission decreased to 27%, and all asymptomatic transmission decreased to 51%.
When researchers broadened the range of components (peak infectiousness days and transmission from asymptomatic individuals), the results showed that at least 50% of COVID-19 infections were caused by persons without symptoms at the time of transmission.
“In addition to identification and isolation of persons with symptomatic COVID-19, effective control of spread will require reducing the risk of transmission from people with infection who do not have symptoms,” the researchers concluded. “These findings suggest that measures such as wearing masks, hand hygiene, social distancing, and strategic testing of people who are not ill will be foundational to slowing the spread of COVID-19 until safe and effective vaccines are available and widely used.”
—Audrey Amos, PharmD
Reference:
Johansson MA, Quandelacy TM, Kada S, et al. SARS-CoV-2 transmission from people without COVID-19 symptoms. JAMA Netw Open. 2021;4(1):e2035057. doi:10.1001/jamanetworkopen.2020.35057