Research shows isolation of asymptomatic cases key to reduce COVID-19

Lung tissue (left) from a person who died of COVID-19 shows the presence of multiple types of immune cell (coloured dots, right).Credit: David A. Dorward & Christopher D. Lucas

A new modeling analysis of COVID-19 transmission data attributed to “silent” infections has suggests that even isolation of all symptomatic individuals may be insufficient to suppress outbreaks.

According to the study, published by the Proceedings of the National Academy of Sciences on Monday, at least one-third of asymptomatic cases would need to be detected and isolated in order to reduce the attack rate below one percent.

“Silent” infections refer to people who either are in the presymptomatic stage or have asymptomatic infections.
In the absence of population-wide restrictions, isolation of infected individuals is key to curtailing transmission. However, the effectiveness of symptom-based isolation in preventing a resurgence depends on the extent of presymptomatic and asymptomatic transmission, said the study.

Researchers from Canada and the United States evaluated the contribution of presymptomatic and asymptomatic transmission based on recent individual-level data regarding infectiousness prior to symptom onset and the asymptomatic proportion among all infections.

They found that the majority of incidences may be attributable to silent transmission from a combination of the presymptomatic stage and asymptomatic infections.

“Consequently, even if all symptomatic cases are isolated, a vast outbreak may nonetheless unfold,” said the study.

The results indicate that symptom-based isolation must be supplemented by rapid contact tracing and testing that identifies asymptomatic and presymptomatic cases, in order to safely lift current restrictions and minimize the risk of resurgence, according to the study.