Bruce Aylward, an epidemiologist who led an advance team from the World Health Organization (WHO), speaks during a press conference of the China-WHO joint expert team in Beijing, capital of China, Feb. 24, 2020. (Xinhua/Xing Guangli)

Dr. Bruce Aylward, senior advisor to the WHO director-general and lead of the COVID-19 international experts' mission in China, said China is passing a "milestone" since it reported no local COVID-19 infections, though 20 days without local transmission doesn't mean it doesn't have the virus.

"But it provides an opportunity to reflect a little bit on what we saw when we were in China," Aylward said.

China's success today, he said, can be attributed to three aspects -- namely investment at the state level in the public health infrastructure, the sense of individual responsibility among the Chinese people, and the incredible effort to build additional capacity and preparedness even when infection was heading down.

"I think all of those things are part of the reason that we're seeing today the very low levels of transmission that hopefully can be maintained," he added.