Until now, evidence suggested that up to half of COVID-19 patients are asymptomatic "silent spreaders" of the disease who were unwittingly contributing to outbreaks. Some estimates even pegged the rate of asymptomatic infections as high as 81%.
Now, new evidence suggests that just 17% of those infected with COVID-19 will experience no symptoms, according to Nature, citing a meta-analysis of 13 studies published last month which involved 21,708 people. What's more, asymptomatic individuals are 42% less likely to transmit the virus than those with symptoms.
The research, spearheaded by lead author Oyungerel Byambasuren of the Institute for Evidence-Based Healthcare at Bond University in Gold Coast, Australia, defined asymptomatic people as those who showed none of the key COVID-19 sysmptoms during the entire follow-up period. The authors only included studies which followed participants for at least seven days, as evidence suggests symptoms typically develop in 7-13 days (during which people are still contagious).
One reason that scientists want to know how frequently people without symptoms transmit the virus is because these infections largely go undetected. Testing in most countries is targeted at those with symptoms.
As part of a large population study in Geneva, Switzerland, researchers modelled viral spread among people living together. In a manuscript posted on medRxiv this month2, they report that the risk of an asymptomatic person passing the virus to others in their home is about one-quarter of the risk of transmission from a symptomatic person. -Nature
That said, the analysis acknowledges that while there is a lower risk of transmission among asymptomatics, they may still present a public health risk due to the fact that they are more likely to be out in the community vs. isolating at home, according to Switzerland-based infectious-disease specialist Andrew Azman of Johns Hopkins Bloomberg School of Public Health, a co-author on the study.
"The actual public-health burden of this massive pool of interacting ‘asymptomatics’ in the community probably suggests that a sizeable portion of transmission events are from asymptomatic transmissions," he said.
Nature notes that other researchers disagree over the extent to which asymptomatic spread contributes to community transmission. " Byambasuren, the lead author, says that if the studies are correct that asymptomatic people are a low transmission risk, "these people are not the secret drivers of this pandemic," as they are "not coughing or sneezing as much" and are "probably not contaminating as much surfaces as other people."
So, while the 'silent spread' factor appears to be far less pronounced than previously thought, and the virus kills less than 1% of those infected under the age of 60, one still has approximately a 10% chance of becoming a "long hauler" - an infected person who essentially suffers from waves of flu symptoms for months on end. Is that worth shutting down the economy over?