Chinese respiratory disease expert Zhong Nanshan on Friday called for sustained international collaboration in the battle against the COVID-19 pandemic and greater attention to asymptomatic cases, citing relatively strong infectivity.

Zhong, an academician at the Chinese Academy of Engineering, made his remarks in his congratulatory letter to the Program of the Congress on COVID-19: Pandemic of the 21st Century, an academic forum that was held in Guangzhou, capital of Guangdong province, on Friday. More than 50 experts and officials from China and Russia participated in the event.

"COVID-19 is still spreading globally, and the nations and regions around the world should join hands to fight against the pandemic, formulating long-term response strategies," he said.

"China and Russia, both adhering to the concept of a community of a shared future for mankind, have good cooperation in pandemic control and prevention, clinical treatment and drug research and development, forming a model of global anti-pandemic cooperation," Zhong said.

He said he hoped this international academic exchange would continue to help build a deep and effective platform for the prevention and control of the pandemic in both nations. Zhong also said he hopes it will help uncover more scientific and effective pandemic prevention and control measures and contribute more to an early end of the spread of the novel coronavirus around the world.

Further, Zhong urged relevant departments to more carefully handle asymptomatic patients who now account for 20 to 40 percent of the total cases.

"Asymptomatic cases have strong infectivity," he said via video while addressing the opening ceremony of the forum.

Regarding responses to infection clusters with undetermined sources, he said universal testing among affected communities is necessary.

And speaking about infectivity, Zhong acknowledged that it's possible, but not common, for patients who have recovered to become reinfected.

He shared two possible explanations for this phenomenon: the first is that the number of antibodies produced after the first infection decline rapidly; the second is that there is either a weak or no antibody response during the first infection, making the patient incapable of resisting the second.

Vladimir Chulanov, chief infection disease specialist at the Ministry of Healthcare of the Russian Federation, said China has done a good job fighting against COVID-19.

Russia has strengthened its own COVID-19 response after learning from China's successful experiences, he said.

Many Chinese counterparts have shared their own established experiences with Russian peers, he said.

The event was jointly organized by Guangdong Pharmaceutical University and Bashkir State Medical University.

It was directed by the Department of International Cooperation and Exchange of the Ministry of Education and is supported by the Association of Sino-Russian Medical Universities. Senior medical experts from both countries attended the event.