A recent analysis by Scripps Research, looking at data available in public databases, shows that up to 45% of people infected by the novel coronavirus that causes COVID-19 have no symptoms of the disease.

The findings, recently published in Annals of Internal Medicine, suggest that asymptomatic infections may have played a significant role in the early and ongoing spread of COVID-19 and highlight the need for expansive testing and contact tracing to mitigate the pandemic.

Scripps researcher Dr. Eric Topol, M.D., and behavioral scientist Daniel Oran, Topol collected information from  nursing home residents, cruise ship passengers, prison inmates and various other groups around the world.

“What virtually all of them had in common was that a very large proportion of infected individuals had no symptoms,” says Oran. “Among more than 3,000 prison inmates in four states who tested positive for the coronavirus, the figure was astronomical: 96 percent asymptomatic.”

Their findings are similar to a study published by the Imperial College of London.  One of the conclusions of both studies is that even people with no symptoms are very efficient at spreading the novel coronavirus.   The Scripps researchers also found that despite no symptoms, some of those infected have lung issues, shown in CT scans, that were apparently created by the virus.  They note that more research is needed about that finding.  The researchers point out that wearing a mask to protect others–since one may not know they have COVID-19–“makes a lot of sense.”

The Scripps researchers shared a short video: