The World Health Organization’s Maria Van Kerkhove, MD and technical lead for the WHO’s pandemic response, caused a stir recently when she implied that transmission of the coronavirus from asymptomatic individuals appears to be “very rare.”
Now, the WHO has sought to clarify her comments, saying they were based on a relatively small set of studies.
Kerkhove’s comments caused confusion because they appeared to directly contradict advice from several public health organizations.
While evidence suggests that individuals with symptoms are most infectious, others do not develop any symptoms at all, despite testing positive for SARS-CoV-2. What remains unknown is how many other people these asymptomatic individuals go on to infect.
It’s one of the reasons why Europe-wide lockdowns have been so effective in halting the spread of the virus, saving millions of lives.
Then there are people who infect others while they are pre-symptomatic, meaning before they have actually developed any symptoms but later do. According to the United States Centers for Disease Control and Prevention (CDC), pre-symptomatic individuals account for around 40% of coronavirus transmission.
Director of the WHO's health emergencies programme, Dr Michael Ryan, said he was "absolutely convinced" that asymptomatic transmission was occurring; "the question is how much".
So the bottom line seems to be that we simply don’t know how big a role asymptomatic individuals play in the spread of the virus. More research is needed.