Michael Ryan, executive director of the World Health Organization’s (WHO) Health Emergencies Programme, called for an open mind on Monday when speculating on the source of the global COVID-19 pandemic as case zero might not be from Wuhan.

In a regular briefing of the WHO, Ryan pointed out that the first cluster of COVID-19 were picked up in Wuhan, yet case zero is not always where the first cluster is, but it’s usually before in time, and might be in another place. Ryan made the remarks citing his 25 years of professional experience.

Ryan said coronavirus is proving it to be exceptionally difficult to detect or stop, but it is important to find the initiation point where the disease crossed the animal-human species barrier.