The outbreak of Delta variant of the coronavirus in Nanjing will be under control in a few weeks, Zhong Nanshan, the country's top epidemiologist, said on Saturday.

He also released the latest research results confirming the effectiveness of the China-made vaccine against the mutated virus.

At a conference on indoor air purification held in Guangzhou, Zhong summarized the features of the Delta infections in Nanjing and gave his conclusions on containing its spread.

Compared with the sporadic outbreak in Guangzhou in May, the situation in Nanjing was more complicated, Zhong said, noting the wider distribution of infections.

Regarding the Delta variant, the concept of close contact was also updated, because the new variant comes with a higher viral load in a person's body and is much more contagious, Zhong said.

Zhong said the definition of close contact for Delta has been expanded to include any person with exposure to a confirmed case in the same room, workplace or building within four days of the onset of symptoms. The update has led to a significant change in management methods.

Recently, the severity and contagion of the Delta variant has raised concerns about the efficacy of Chinese-made vaccines. Zhong shared research results based on preliminary statistics from Delta patients in Guangzhou showing that China's vaccines offered protection against the new virus.

The protective effect of China's vaccine in cases of severe symptoms was 100 percent, and protection for moderate, mild, and asymptomatic patients was 76.9 percent, 67.2 percent, and 63.2 percent, respectively.

None of the 13 severe patients in previous outbreaks in Guangzhou had been vaccinated, Zhong said.

To defeat the pandemic, Zhong emphasized protective measures in communities and the establishment of herd immunity. In China, herd immunity may be achieved after 83.3 percent of Chinese people are inoculated, Zhong said.

Feng Xiaojie contributed to this story.