Silent transmission is the idea that those who are infected with COVID-19 but show no symptoms can still spread the virus to other people. A number of early studies—in some cases affected by limitations that may have led to their proportion of presymptomatic transmission to be "artifactually inflated"—suggested that silent transmission accounted for around half of secondary infections, or even more.
Initially, "we didn’t realize the extent of asymptotic spread," Dr. Fauci said in July 2020, adding that later, "we fully realized that there are a lot of people who are asymptomatic who are spreading infection. So it became clear that we absolutely should be wearing masks consistently," Dr. Fauci said at the time.The new study, published in the August issue of The Lancet’s Microbe journal, shows that people who are sick with COVID-19 but don’t show any symptoms have a limited ability to spread the virus to other people.
Participants in the British study, which was carried out by researchers at Imperial College London, were unvaccinated healthy adults aged 18-30 who were intentionally infected with COVID-19.
The subjects were monitored under controlled circumstances while self-reporting symptoms three times per day, and researchers collected nose and throat swabs from them daily, checking for the presence of the virus.
Another study from July 2020 called "The Implications of Silent Transmission for the Control of COVID-19 Outbreaks" went even further, suggesting that people were most infectious during the presymptomatic phase and concluding that silent transmission was the "primary driver of COVID-19 outbreaks and underscore the need for mitigation strategies, such as contact tracing, that detect and isolate infectious individuals prior to the onset of symptoms." That study relied on a range of assumptions and models, with different presymptomatic, asymptomatic, and symptomatic transmission rates calculated based on a complex mathematical model from another study.
Findings from earlier studies like the ones cited above led public health officials to argue that silent spreaders were a big factor in COVID-19 transmission and so to recommend that everyone should mask up.
