Study Says Half of Coronavirus Cases Might Be From “Silent Spreaders”

Study Says Half of Coronavirus Cases Might Be From “Silent Spreaders”

Another reason to be cautious.


People who showcase no symptoms are likely key drivers of the novel coronavirus spread, according to a study published in the Proceedings of the National Academy of Sciences.

Alison Galvani, director of Yale University’s Center for Infectious Disease Modeling and Analysis, and colleagues tapped into coronavirus transmission models to determine the extent to which silent transmission contributes to the contagion’s spread.


The team based the study on existing research that indicates asymptomatic infections account for 17.9% to 30.8% of all coronavirus infections. Assuming 17.9% of cases are asymptomatic, the researchers discovered that pre-symptomatic individuals would account for 48% of transmissions, and asymptomatic people would be responsible for 3.4%.

If 30.8% of cases are asymptomatic, the team found that pre-symptomatic people would account for 47% of transmissions, while those who are asymptomatic would be responsible for 6.6%.

“We found that the majority of incidences may be attributable to silent transmission from a combination of the pre-symptomatic stage and asymptomatic infections. Consequently, even if all symptomatic cases are isolated, a vast outbreak may nonetheless unfold,” the researchers said in the study.

“We further quantified the effect of isolating silent infections in addition to symptomatic cases, finding that over one-third of silent infections must be isolated to suppress a future outbreak below 1% of the population.”

The researchers noted that, along with symptom-based isolation, there needs to be improved contact tracing and testing that identifies both asymptomatic and pre-symptomatic cases.

“Our results indicate that silent disease transmission during the pre-symptomatic and asymptomatic stages are responsible for more than 50% of the overall attack rate in COVID-19 outbreaks. Furthermore, such silent transmission alone can sustain outbreaks even if all symptomatic cases are immediately isolated,” the researchers said.

According to Johns Hopkins University data, thirty-one states are reporting higher rates of new coronavirus cases this week compared to last week. Only four states have witnessed fewer cases.

“We are still knee-deep in the first wave of this,” White House Coronavirus Task Force member Dr. Anthony Fauci said during a recent Facebook/Twitter livestream event.

“And I would say this would not be considered a wave. It was a surge, or a resurgence of infections superimposed upon a baseline … that really never got down to where we wanted to go. So, it’s a serious situation that we have to address immediately.”

Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek and Arirang TV. Follow or contact him on LinkedIn.

Image: Reuters