Expert clarifies on role of silent spreaders of coronavirus disease

A top World Health Organization (WHO) expert tried to clear up on Tuesday “misunderstandings” about comments she made that were widely understood to suggest that people without symptoms rarely transmit the coronavirus disease (Covid-19). This comment had immediately triggered scepticism from health experts around the world.

Maria Van Kerkhove, the UN health agency’s technical lead on the pandemic, insisted that she was referring only to a few studies, not a complete picture, in the comments she made on Monday. On Tuesday, she said some studies showed that asymptomatic careers could spread the disease.

Van Kerkhove’s remarks on Monday raised questions among outside experts and health officials who have recommended that people wear masks to try to prevent the virus from spreading.

“That’s a tiny subset of studies,” she said. “I used the phrase ‘very rare’, and I think that that’s (a) misunderstanding to state that asymptomatic transmission globally is sporadic. What I was referring to was a subset of studies.”

The clarification, which came during a WHO social-media chat, showed questions remain about whether infected people who don’t show symptoms can transmit the virus to others. Critics of the agency have previously pointed to WHO’s position on wearing masks as an example of inadequate policy recommendations. The agency said for months that wearing masks would not contain the virus, a place that it changed last week.

A second WHO official, in comments to HT, sought to make a distinction between asymptomatic and pre-symptomatic transmission. “Sars-CoV2 transmission is associated with a high virus load in the upper respiratory tract. While a proportion of people (around 15 to 20%) are asymptomatic, most transmission seems to occur from those with symptoms. However, we have to be careful because people can be infectious one to two days before they develop symptoms, so right now it is important for everyone to wear face coverings when they cannot maintain physical distancing,” said Dr Soumya Swaminathan, chief scientist, WHO, Geneva.

On Tuesday, before Van Kherkhove’s clarification, experts urged caution. “The knowledge gaps are there, but there are too many contradictory statements from there WHO that are confusing countries, particularly those with limited technical capabilities. The latest statement about the asymptomatic transmission being rare will create more confusion in an already volatile situation,” said K Sujatha Rao, former health secretary, ministry of health and family welfare.

Dr Ashish K Jha, director at the Harvard Global Health Institute, said on Twitter some models “suggest 40-60% of spread was from people when they didn’t have symptoms”.