It will take at least two to three years before the world can achieve herd immunity against COVID-19 through mass vaccination, leading Chinese respiratory disease expert Zhong Nanshan said Tuesday.

He made the remarks during a rare online exchange with top U.S. infectious disease expert Anthony Fauci hosted by the University of Edinburgh.

Zhong, a key expert behind China's quick and successful containment of the epidemic, stressed that herd immunity worldwide can only be achieved when the majority of the global population gets vaccinated against the virus.

He warned against "natural immunity," which means letting 60 to 70 percent of people get infected with the virus without any intervention. It's unrealistic, less scientific and inhumane, as 2 to 3 percent of those infected globally (14 to 21 million people) would die, he said. 

International cooperation crucial to end COVID-19

At the hour-long event, the two experts shared their views of the ongoing COVID-19 pandemic and explored how to change and reshape public health systems to transform outcomes.

Both of them agreed that international cooperation is crucial to put an end to the global health crisis.

Zhong said that the coronavirus is the enemy of mankind. As long as it is still spreading in some countries, it has not ended for the whole world. He called for all countries to maintain the spirit of solidarity, enhance cooperation, and work together to vaccinate as many people as possible.

Fauci pointed out another reason why global cooperation is so important is that the virus could mutate quickly in cross-border transmissions, which would in turn impact countries that have successfully controlled the pandemic.

Zhong agreed that new variants of the coronavirus pose big challenges to the prevention and control of the pandemic, and will greatly undermine the effectiveness of existing vaccines.

Therefore, global cooperation is needed to further relative studies and develop better vaccines that work against the variants, he said.

Concerns for the future

The two experts also shared their concerns about the future global public health systems.

Zhong said he feared political reasons might still be in the way of decision-making when it comes to health problems in the future. He called on policymakers in all countries to take decisive actions based on science, evidence and clinical trials.

What Fauci feared is that mankind would forget about the horrible experiences that they had gone through and not draw lessons from them. 

(Video by CGTN's Zhao Yunfei.)