A driver who finished quarantine leaves Xinfadi market in Fengtai District of Beijing, capital of China, July 11, 2020. From Saturday, the second batch of people at high risk of exposure to the Xinfadi market are released from quarantine. (Xinhua/Zhang Chenlin)

The COVID-19 strain taken from samples of the confirmed case found in North China's Tianjin shows that the virus belongs to the L genotype of the European branch, sharing a high similarity to the confirmed cases in Beijing's Xinfadi market and Hebei Province from June to July. 

Analysis conducted by the Tianjin Center for Disease Control and Prevention on two virus samples, one confirmed case and one asymptomatic, showed that the strains belonged to the L genotype of European branch.

It is now confirmed that the virus of the outbreak in the Xinfadi wholesale market in Beijing, the four confirmed cases in Hebei Province in June, and the three local cases in Tianjin all belonged to the same European branch.

Wu Zunyou, the chief epidemiologist at the CDC, told media that early investigations showed the COVID-19 cases were mainly related to frozen seafood section in the Huanan seafood market. Wu said customs authorities in many cities across the country found virus-contaminated frozen food imports, presenting growing evidence that frozen seafood or meat may introduce the virus from affected countries into China.

Yang Zhanqiu, deputy director of the pathogen biology department at Wuhan University, told the Global Times on Thursday that the strong and long duration of the virus in the European branch is critical for the coming winter, and strict control of imported cases from abroad is needed to prevent a second wave in China.

So far, a total of 8,819 close contacts have been investigated in Tianjin, and 960 people are still under medical observation.