China is going all out to develop vaccines against the mutated novel coronavirus, the country's top respiratory expert Zhong Nanshan said on Saturday.

Zhong said at a medical science forum in south China's Guangzhou City that the main problem people are currently experiencing is the virus variants.

Variants have been found in many countries, including the UK, Brazil and South Africa. The variants are mostly believed to be more contagious.

Existing inactivated vaccines in use are found to be less effective against the B.1.351 variant first detected in South Africa, Zhong said.

He added that there are still quite a lot of questions regarding the COVID-19 vaccines. For example, how long does the immunity from the COVID-19 vaccination last? Whether getting additional doses can help improve the protection rate against the virus? Such questions remain to be resolved.

There are nearly 50 types of COVID-19 vaccines under development in China and more than 200 worldwide, Zhong said, adding that an important issue is to find out which kind of vaccine is more beneficial to epidemic prevention and control.

He said he's also concerned about the reported side effects of COVID-19 vaccines worldwide. For instance, more than 30 people in Germany, Austria, and the UK suffered blood clots and thrombocytopenia after getting vaccinated. He said such questions as to why this happened and how the side effects can be avoided urgently need to be addressed.