Chinese COVID-19 vaccines were effective in the prevention and control of recent local outbreaks in Nanjing, Yangzhou and Zhengzhou, an official with the National Health Commission said on Friday.

Zheng Zhongwei, head of China's COVID-19 vaccine development task force, said statistics from recent clusters show people who have inoculated two doses of vaccines account for less than 5 percent of severe cases.

"That means more than 95 percent of patients with severe symptoms have not been vaccinated or completed the full immunization procedures," Zheng said.

He added none of the 53 severe cases in Yangzhou, Jiangsu province have been vaccinated.

"It's obvious COVID-19 vaccinations are effective in the prevention and control of recent clusters," Zheng said.

Given that this wave of cases in Jiangsu and Henan provinces are of the more infectious Delta variant, Zheng said a study on the previous epidemic in Guangdong province, led by academician Zhong Nanshan, shows the protection effect of two doses' vaccination reached 70 percent on moderate cases of Delta variants while that of severe symptoms reached 100 percent.

Another study conducted by the Guangdong Provincial Center for Disease Control and Prevention found the viral load of people who have not been vaccinated or only received one dose was triple those who completed vaccination, Zheng said.

"The vaccinated population's risk of infecting others is also reduced," he said.

Zheng also stressed no vaccine in the world is 100 percent effective.