Residents take nucleic acid tests in Zhenhai district, Ningbo, East China's Zhejiang Province, on December 12, 2021. Photo: VCG

The virus behind the latest round of the COVID-19 epidemic in Ningbo, East China's Zhejiang Province, has been identified as the Delta strain. The outbreak is linked to a flareup in neighboring provinces and cities, according to the city's authorities.

In a news conference Sunday, Ningbo officials said that, after sequencing results of specimens from cases at the Ningbo CDC, the virus causing the COVID-19 epidemic in the city is the AY.4 variant, a sub-lineage of the Delta variant.

As of Sunday, Ningbo has reported a total of 44 confirmed cases in the current outbreak, with ages ranging between 2 and 70.

Ningbo officials said the chain of transmission in this outbreak is relatively clear and all belong to the same chain. 

The virus first spread within families and then from relatives to coworkers, causing multiple infections in a care center. The infections then happened in families and communities of those infected in the center, officials said. 

In a news conference on Saturday, the State Council, China's Cabinet, announced that the recent domestic COVID-19 outbreaks in Zhejiang, Shanghai and Jiangsu are related and have very similar genome sequences. 

There have been no reports of COVID-19 infections caused by the Omicron strain in the Chinese mainland.