Jan. 11, 2021 -- More than half of all COVID-19 cases transmit from people who don’t have any symptoms, according to a model developed by CDC researchers.
About 59% of transmission comes from people without symptoms, according to a new study published Thursday in JAMA Network Open. This includes 35% from people who infect others before they show symptoms and 24% from people who never develop any symptoms.
“The bottom line is controlling the COVID-19 pandemic really is going to require controlling the silent pandemic of transmission from persons without symptoms,” Jay Butler, one of the study authors and the CDC deputy director for infectious diseases, told The Washington Post.
Testing and isolating people with symptoms won’t control the ongoing spread of the pandemic, the authors wrote, emphasizing the importance of universal face masks, hand hygiene, social distancing, and strategic testing of people who aren’t sick. With new contagious variants circulating around the world and in several states, that’s even more important, Butler added.
“Those findings are now in bold, italics and underlined,” he said. “We’ve gone from 11-point font to 16-point font.”
The research team created a mathematical model to analyze different scenarios, such as shifting the peak time of infectiousness. Consistently, the model predicted that asymptomatic transmission accounted for at least half of COVID-19 cases.
Even still, the research team noted that COVID-19 transmission is complex and could vary for numerous reasons. The environment, for instance, could shift whether asymptomatic transmission is more prevalent. People in long-term care facilities and congregate settings may face a higher risk of contracting the virus or transmitting it to others.
“In the absence of effective and widespread use of therapeutics or vaccines that can shorten or eliminate infectivity, successful control of SARS-CoV-2 cannot rely solely on identifying and isolating symptomatic cases,” they wrote. “Even if implemented effectively, this strategy would be insufficient.”