(Yicai Global) Oct. 19 -- High-ranking Chinese scientists have called for more studies on how long antibodies last after a Covid-19 infection and whether an antibody mechanism familiar from other viruses can cause a second infection.

The medical community is having more knowledge about Covid-19, but vaccine and drug developers still face issues such as the duration of neutralizing antibodies and antibody-dependent enhancement, Gao Fu, director of the Chinese Center for Disease Control and Prevention, said at a virology conference held over the weekend.

As dengue and Ebola viruses have shown, those who have already recovered from a certain virus can fall sick again by a mechanism that makes the previously produced antibodies help a new virus enter. That is called antibody-dependent enhancement. But it is unclear whether Covid-19 does that.

Current studies haven't discovered ADE, but more data are needed, top experts told Yicai Global.

"Reinfections worldwide cannot directly be related to the ADE phenomenon, because severe reinfections are not necessarily caused by antibodies," Ying Tianlei, researcher at the Shanghai Medical College of Fudan University, said to Yicai Global.

One way that scientists can protect vaccine receivers is by making better products. Research teams must choose antigens which have a stable virus protein that should not cause ADE so easily since the risk cannot be ruled out, Ying added.

Medical companies are racing to come up with an inoculation to control the Covid-19 pandemic. China only had 11 vaccines in clinical trials as of Sept. 25, and four of them in phase III. The country is expected to produce 610 million doses annually by the end of this year and more than 1 billion doses next year.

But safety first, scientists say. Although a recent study on 184 inactivated vaccine recipients in China found out that recipients' antibodies had not declined not significantly, the world needs more research on the risk of reinfection, said Zhang Wenhong, head of the infectious diseases department at Shanghai's Huashan Hospital.

Editor: Zhang Yushuo, Emmi Laine