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About 80% of people infected with the novel coronavirus don’t spread the infection to anyone else, leaving the so-called super spreaders as the drivers of the global pandemic that has infected more than 5 million Americans alone, killing 162,000 people.

Preliminary research from the Fred Hutchinson Cancer Research Center suggests that infected people are most contagious for a short window, perhaps only two days, when their virus load is high. Unfortunately, that period also appears to strike before they’re symptomatic for COVID-19.

“The ethical thing to do as an individual is to walk around with the assumption that you’re infectious and contagious, and that it’s your responsibility to protect the public. That doesn’t change at all,” said Dr. Joshua T. Schiffer, an infectious diseases physician and author of the research, in a statement.

The findings emphasize the importance of readily available, rapid tests to identify infections.

Infected people are likely spreading very small amounts of the virus over a longer period, possibly for weeks, but at levels that don’t sicken others. But when a person in a highly contagious state is in contact with a larger group of people, particularly in an indoor space or a situation where people aren’t using masks, the disease can take off.

The scientists ran roughly half a million simulations of the spread of the disease and matched them against data on actual COVID-19 infections. They reported that both influenza and COVID-19 have short windows during which they’re infectious, but the novel coronavirus’ ability to spread as an aerosol that is exhaled, coughed or sneezed appears to amplify its infectiousness. The researchers concluded that “approximately 10-20% of infected people account for 80% of SARS-CoV-2 transmissions.”

The research was posted Friday on MedRxiv, a platform for sharing studies before it goes through a rigorous peer review, giving scientists quicker access to the findings and a chance to discuss the results.

 

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