In a new study, researchers found that transmission of severe COVID-19 from asymptomatic people accounts for about half of all transmissions.
The research was conducted by a team from the U.S. Centers for Disease Control and Prevention.
The team examined the proportion of SARS-CoV-2 transmissions in the community that likely occurred from asymptomatic individuals.
The relative amount of transmission was assessed from presymptomatic, never symptomatic, and symptomatic individuals across a range of scenarios.
The assumptions for the model were that peak infectiousness was at the median of symptom onset, 30% of people with infection remain asymptomatic, and 75% as infectious as those who develop symptoms.
Based on these assumptions, the researchers inferred that about 24% of all transmission was accounted for by persons with infection who never developed symptoms.
In this base case, 59% of all transmission came from asymptomatic individuals: 35% and 24% from presymptomatic people and people who remain asymptomatic, respectively.
At least 50% of new SARS-CoV-2 infections were estimated to have originated from exposure to infected, but asymptomatic, people under a broad range of values for each of these assumptions.
These findings suggest that effective control also requires reducing the risk of transmission from people with infection who do not have symptoms.
One author of the study is Michael A. Johansson, Ph.D.
The study is published in JAMA Network Open.
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