Learning COVID's origins will take years: WHO investigator

Dwyer said the team in Wuhan had received the access it requested from Chinese authorities as it tries to understand the early days of the novel coronavirus outbreak first identified in Wuhan.

"Everybody knows how it really exploded out of Huanan market in Wuhan, but the key is what was happening around that time and before," Dwyer said.

The origin of the coronavirus has become highly politicized following accusations that China was not transparent in its early handling of the outbreak. Beijing has pushed the idea that the virus could have originated elsewhere.

Dwyer, an Australian specialist in HIV/AIDS who previously worked with the WHO during the SARS and avian flu outbreaks, said the "conundrum" of COVID-19 was that early asymptomatic carriers may not have known they had it.

"It would be naive to think that we're going to get virus zero," Dwyer said.