The World Health Organization (WHO) has said the fact that Wuhan's specific surveillance system was triggered by COVID-19 doesn't necessarily mean that that is where the disease originated. 

"One must remember that there was a specific surveillance system in place in Wuhan for picking up clusters of atypical pneumonia," said Michael Ryan, executive director of WHO Health Emergencies Programme.

"It was there for a very specific purpose. And the fact that that fire alarm was triggered doesn't necessarily mean that that is where the disease crossed from animals into humans."

The WHO has sent two experts to China to find out more about the origin of the virus.

On Monday, WHO Director-General Tedros Adhanom Ghebreyesus said: "The WHO advance team that traveled to China has now concluded their mission to lay the groundwork for further joint efforts to identify the virus origins.

"As a result of these efforts, WHO and Chinese experts have drafted the Terms of Reference for the studies and program of work for an international team, led by WHO. The international team will include leading scientists and researchers from China and around the world."

Ghebreyesus added that there may never be a "silver bullet" in the form of a perfect vaccine, but he called on nations to "do it all."

The new slogan urges countries to rigorously enforce health measures such as mask-wearing, social distancing, hand-washing and testing.

Chinese Foreign Ministry briefs on WHO experts' work in China 

At a press briefing on Tuesday, Chinese Foreign Ministry spokesperson Wang Wenbin said the two experts from WHO had been in China from July 11 to August 2, having many discussions with Chinese experts during their stay.  

They had in-depth exchanges on the progress of scientific research work and the next research plan for COVID-19 in terms of crowd handling, environment, animal tracing and transmission route.  

Experts from both sides worked out the China part of the global COVID-19 scientific cooperation plan, and further studied the animal source, intermediate host and transmission route of the coronavirus to better prevent and control the COVID-19 epidemic, Wang added. 

(Video editor: Natalia Luz）