WHO: asymptomatic spread of COVID-19 rare

The spread of Covid-19 by someone who is not showing symptoms appears to be rare, the World Health Organization's technical lead for coronavirus response and head of the emerging diseases and zoonoses unit, Maria Van Kerkhove, said.

"From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual," Van Kerkhove said during a media briefing in Geneva.

"We have a number of reports from countries who are doing very detailed contact tracing. They're following asymptomatic cases, they're following contacts and they're not finding secondary transmission onward. It is very rare - and much of that is not published in the literature," she said. 

"We are constantly looking at this data and we're trying to get more information from countries to truly answer this question. It still appears to be rare that an asymptomatic individual actually transmits onward."

Van Kerkhove went on to describe how the novel coronavirus, a respiratory pathogen, spreads through droplets, which can be released when someone coughs or sneezes.

"It passes from an individual through infectious droplets. If we actually followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those cases, we would drastically reduce -- I would love to be able to give a proportion of how much transmission we would actually stop -- but it would be a drastic reduction in transmission," she said.

Van Kerkhove also said that what appear to be asymptomatic cases of Covid-19 often turn out to be cases of mild disease.\

"When we actually go back and we say how many of them were truly asymptomatic, we find out that many have really mild disease," CNN cited Van Kerkhove as saying.

"They're not quote-unquote Covid symptoms, meaning they may not have developed fever yet, they may not have had a significant cough, or they may not have shortness of breath - but some may have mild disease," she said. "Having said that, we do know that there can be people who are truly asymptomatic."