The World Health Organization walked back comments made Monday when one of its top scientists said transmission of the coronavirus by people who never developed symptoms is “very rare,” which drew skepticism from physicians and others across social media. 

That admission sent shock waves throughout the world, much of which has been locked down for months for fear of spreading the virus by people who show no signs of illness. 

Dr. Maria Van Kerkhove, head of the WHO’s emerging diseases and zoonosis unit, said Tuesday that asymptomatic spread is a “really complex question” and much is still unknown. “We don’t actually have that answer yet,” she said.

“I was responding to a question at the press conference. I wasn’t stating a policy of WHO or anything like that. I was just trying to articulate what we know,” she said on a live Q&A streamed across multiple social media platforms. “And in that, I used the phrase ‘very rare,’ and I think that that’s misunderstanding to state that asymptomatic transmission globally is very rare. I was referring to a small subset of studies.”