Selective: Asymptomatic COVID Transmission

Misbar discovered that while we are learning more about COVID-19 transmission by people without symptoms, the topic can still create confusion and uncertainty. It appears that approximately 20 percent of people with COVID-19 infections are without symptoms, or asymptomatic according to bmj.com. However, when considering COVID-19 transmission, it is important to separate truly asymptomatic individuals, from those who do not have symptoms initially, but then develop symptoms a few days later according to Dr. Maria Van Kerkhove of the World Health Organization (WHO). 

For people who are COVID-19 positive and never develop symptoms, transmission of the disease to others is much less likely than for those with symptoms. While more information is needed to fully understand what role those without symptoms play in spreading COVID-19, there are several reasons why they would be less infectious. One reason is that just because someone tests positive for COVID-19, they may or may not have an active infection with live virus. And it appears the duration of time spent shedding the virus is shorter in people who are asymptomatic. In other words, they clear the virus from their bodies faster.  

Another reason that asymptomatic people may be less likely to be contagious is the fact that COVID-19 is a respiratory virus and spreads easily through coughing. If a person is asymptomatic, they are not coughing or have a runny nose, so transmission may be less likely. 

On a WHO FaceBook Live broadcast on June 9, 2020, Kerkhove addressed the issue specifically. She stated that based on the small sampling of studies they have viewed to date, transmission by asymptomatic people appears to be very rare. Based on models (mathematical estimations, not real cases), there is a range, and COVID-19 transmission by asymptomatic people could be around 40 percent. According to some other research, asymptomatic people are about 40 percent less likely to transmit the virus compared to people with symptoms. 

While there is much yet to be understood about COVID-19, it appears that secondary infection of the disease from a truly asymptomatic person – versus a pre-symptomatic person – is reduced compared to those with symptoms and may only occur rarely in comparison.