The spread of novel coronavirus Covid-19 by someone who is not showing symptoms appears to be rare, Maria Van Kerkhove, the World Health Organization's technical lead for coronavirus response and head of the emerging diseases and zoonoses unit, said during a media briefing in Geneva on Monday.
"From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual," media reports quoting Van Kerkhove.
Some people, particularly young and otherwise healthy individuals, who are infected by the coronavirus never develop symptoms or only develop mild symptoms. Others might not develop symptoms until days after they were actually infected.
Preliminary evidence from the earliest outbreaks indicated that the virus could spread from person-to-person contact, even if the carrier didn't have symptoms. But WHO officials now say that while asymptomatic spread can occur, it is not the main way it's being transmitted.
Van Kerkhove also stated that seemingly asymptomatic carriers just didn't recognize the signs of the virus: "When we actually go back and say, 'How many of them were truly asymptomatic?' we find out that many have really mild disease, very mild disease."
"Comprehensive studies on transmission from asymptomatic individuals are difficult to conduct, but the available evidence from contact tracing reported by Member States suggests that asymptomatically-infected individuals are much less likely to transmit the virus than those who develop symptoms," Van Kerkhove later tweeted.
While the statement drew questions from experts on Twitter, it may simply be an issue of semantics, with Dr Isaac Bogoch and Dr Allan Detsky of the University of Toronto previously pointing out the misuse of the term "asymptomatic" when referring to "presymptomatic" patients.
Dr Ashish K Jha, director at the Harvard Global Health Institute, tweeted out the distinction and noted that the agency "should be clearer in communication, also noting that some models "suggest 40%-60% of spread is from people when they didn't have symptoms."
US Centers for Disease Control and Prevention in early April began recommending people wear cloth face coverings when out in public due to studies that show asymptomatic or presymptomatic people are able to spread the disease as well.
Understanding the characteristics and spread of Covid-19 has been an ongoing challenge throughout the pandemic, as characterized by the continuing questions surrounding the spread of the disease before symptoms set in.
50%. That's the portion of new cases Singapore confirmed on Monday that were symptomless, according to Reuters.
