Nearly 60% of COVID-19 spread may come from asymptomatic spread, model finds

People with COVID-19 who don't exhibit symptoms may transmit 59 percent of all virus cases, according to a model developed by CDC researchers and published Jan. 7 in JAMA Network Open. 

Since many factors influence COVID-19 spread, researchers developed a mathematical approach to assess several scenarios, varying the infectious period and proportion of transmission for those who never display symptoms according to published best estimates.  

In the baseline model, 59 percent of all transmission came from asymptomatic transmission. That includes 35 percent of new cases from people who infect others before they show symptoms and 24 percent from people who never develop symptoms at all. Under a broad range of values for each of these assumptions, at least 50 percent of new COVID-19 infections were estimated to have originated from exposure to asymptomatic individuals. 

The more contagious variant first identified in the U.K. and since found in six states underscores the importance of the model findings, said Jay Butler, MD, CDC deputy director for infectious diseases and a co-author of the study.

"Controlling the COVID-19 pandemic really is going to require controlling the silent pandemic of transmission from persons without symptoms," Dr. Butler told The Washington Post. "The community mitigation tools that we have need to be utilized broadly to be able to slow the spread of SARS-CoV-2 from all infected persons, at least until we have those vaccines widely available."

Whether vaccines stop transmission is still uncertain and was not a scenario addressed in the model. 

More articles on public health:
3 states have highest COVID-19 infection rates in world; UK variant in Pennsylvania — 5 updates
DC hospitals treat victims of Capitol riot: 5 things to know 
24 states where COVID-19 is spreading fastest, slowest: Jan. 7


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