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Asymptomatic and presymptomatic people transmit most COVID-19 infections: Study

ABC News Corona Virus Health and Science

Understanding silent infections may be key to controlling the virus' spread.

Silent transmission of the novel coronavirus could account for more than half of infections, according to one new mathematical model by U.S. and Canadian researchers.

The researchers utilized data on asymptomatic and presymptomatic transmission from two different epidemiological studies and estimated that more than 50% of infections were attributable to people not exhibiting symptoms.

Since the study is based on a mathematical model, the 50% finding is an estimation based on probabilities and approximations, rather than a precise figure.

The findings were published this week in the Proceedings of the National Academy of Sciences of the United States of America.

A different study, published in June in the journal Nature, found that in one Italian town in which the majority of residents were tested for COVID-19 while the town was under a 14-day quarantine, approximately 40% of individuals who tested positive had no symptoms.

The findings could have real-world implications for leaders deciding how to rein in outbreaks in their respective countries or regions.

Widespread testing, isolating infected people, and ordering a community lockdown stopped the Italian outbreak in its tracks, the authors of the Nature study concluded.

"Even if all symptomatic cases are isolated, a vast outbreak may nonetheless unfold," the PNAS study's authors wrote.

"Understanding how silent infections that are in the presymptomatic phase or asymptomatic contribute to transmission will be fundamental to the success of postlockdown control strategies," they said.

What to know about the coronavirus:

  • How it started and how to protect yourself: Coronavirus explained
  • What to do if you have symptoms: Coronavirus symptoms
  • Tracking the spread in the U.S. and worldwide: Coronavirus map

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