Editor's Note: The World Health Organization (WHO) declared COVID-19 a pandemic on March 12. As of April 10, 212 countries and regions worldwide have confirmed over 1,470,000 cases, with more than 87,000 deaths, according to the WHO. CGTN's live program "COVID-19 Frontline" invites medical workers and experts from central China's Wuhan and all over the world to share their experiences and take questions from social media users, in the hope of providing more information to those who are battling against the pandemic.

Is the mortality rate of COVID-19 lower in tropical areas? How does the virus attack the immune system? Can recovered patients test positive for the virus again days after clinical recovery? 

These are some of the questions from international medics to their Chinese counterparts in the fight against COVID-19. In the latest episode of CGTN's live program "COVID-19 Frontline," Chinese doctors from the Second Affiliated Hospital Zhejiang University (SAHZU) answered the questions and shared their firsthand experience with medics and medical experts from the U.S., Pakistan, and Kenya.

Live: Chinese doctors share COVID-19 experience with foreign medics

Is the mortality rate lower in tropical areas?

"According to my observation, the death rate of COVID-19 is quite low in tropical countries compared with the western world. What's your opinion about this?" asked Prof. Intekhab Alam, former chairman of the Department of Medicine, Lady Reading Hospital, which is one of the most important medical institutes in Pakistan. 

Lu Xiao, group leader of SAHZU medical team in Wuhan, said that there has been a study in China that shows the novel coronavirus can survive in a hot and humid environment. It means that a tropical climate does not make a difference to the virus. This is also what distinguishes the novel coronavirus from other common viruses, which usually wane in hot weather, he added.

Prof. Wang Jian'an, president of SAHZU, said he's not sure whether it's a temporary phenomenon. He explained it may be due to lower population density in areas like Africa, and also the younger average age of people, since the COVID-19 infection rate is higher among seniors. 

Dr. Moses Masika, a virologist of the Department of Medical Microbiology, University of Nairobi, Kenya, said that the lower infection and mortality rates in Africa should have something to do with the amount of international travels. He said before the pandemic, among the 100 international travelers, only three are from Africa, which means the risk of African people getting infected is much lower than that of European and American citizens.  

How does the virus affect the immune system? 

Prof. Alam also asked about pathological features of the virus. "Initially we thought it's pneumonia … but recently we find that the virus can affect our immune systems. What's your opinion on that?" he asked.  

Dr. Wu Xuejie, Attending Physician of the Infectious Disease Department at SAHZU, explained the pathogenesis of the virus. "Actually, our immune systems will react to every pathogen that enters our bodies, including viruses and bacteria. Usually, when they enter the body, they will initiate the immune response," he said. 

"If the response is very strong, sometimes it will cause inflammatory factors such as interlukin-6 and interlukin-1, which will elevate to a high level and cause cytokine storm … Sometimes it will cause organ dysfunctions. The most commonly affected organ is lung, and the others include liver, kidney, and heart," he added.  

Can recovered patients test positive for the virus again days after clinical recovery? 

Prof. Benjamin Neuman, head of the Biology Department at Texas A&M University, said that he saw a recent report from Germany that said a small number of patients were tested positive again for the virus after one or two weeks after clinical recovery. He asked whether it's something that also happened in China occasionally. 

Dr. Cui Wei, head of the Expert Panel for COVID-19 Patients in Wenzhou commissioned by Zhejiang Provincial Health Commission, said that China's top COVID-19 expert Dr. Zhong Nanshan reported the same scenario at a press briefing.  

Dr. Zhong said there have been several patients whose nucleic acid tests were positive again after their 14-day quarantine since they were discharged from the hospital but had no symptoms. So the patients were isolated again and the epidemical surveillance was performed again. 

He said the key issue is whether these people can still spread the virus to others, and his team has conducted researches on that, which shows such patients are not contagious to others. A similar conclusion has been reached by some Hong Kong experts in separate studies. 

"This phenomena tell us there may be some viral segment inside the patient's body, but it has no clinical meaning," Dr. Cui said.  

In the later programs, more doctors and experts on the frontline in Wuhan will join in to share their experience with their colleagues from other parts of the world. And for those who have questions or confusions, you can also pose your questions with CGTN using #MyOpinionOnCOVID19 on Facebook.