The World Health Organization walked back a surprise statement that people without symptoms cannot easily spread the novel coronavirus, adding on Tuesday that too much about the virus remains unknown.

“I was responding to a question at the press conference. I wasn’t stating a policy of WHO or anything like that. I was trying to articulate what we know, and in that, I used the phrase ‘very rare.’ And I think that’s a misunderstanding, to state that asymptomatic transmission is very rare,” WHO epidemiologist Dr. Maria Van Kerkhove said Tuesday.