A residential community in Shanghai's Pudong district was announced as a COVID-19 medium-risk region on Tuesday following the emergence of a new case on Monday.

This latest case is the city's first in six months.

The patient is a 53-year-old male who handles cargo flights for a foreign airline company at Pudong International Airport. He did not leave Shanghai in the last 14 days.

Li Guohua, vice-governor of Pudong district, said during a municipal media conference on Tuesday that the case is unlikely to be linked to those in other parts of the country.

"The disease prevention and control department is racing against time to conduct genetic sequencing of the virus that he contracted so as to determine if it is the Delta variant," said Wu Jinglei, director of the Shanghai Municipal Health Commission.

The man was discovered to be infected after he underwent the usual nucleic acid tests that those working in high-risk positions are subjected to, the government said. Previous screenings, including those done on July 21 and July 28, turned out negative.

As of 9 am on Tuesday, 52 close contacts of the case had been identified and put under hotel quarantine. All their initial nucleic acid tests returned negative.

A total of 250 secondary close contacts of the case had also been identified and put under hotel quarantine. All their initial nucleic acid tests returned negative.

In addition, 64,860 relevant individuals had been tested, with 27,174 of them showing negative results so far.

Wu said that more than 18 million residents in the municipality with a permanent population of more than 24 million have received two doses of COVID-19 vaccination as of Monday. The vaccination rate among those above 18 years old is 85 percent.

Zhang Wenhong, leader of the Shanghai team of experts in the clinical treatment of novel coronavirus pneumonia cases, said the vaccination plan will be further expanded.

"It's not surprising that individuals working in high-risk positions may contract the virus when the pandemic is still going on in many parts of the world. No vaccine, including a COVID-19 vaccine, guarantees 100 percent protection," said Zhang.

"But the fact that his coworkers and relevant contacts have tested negative demonstrates that widespread vaccination can largely reduce the speed of the virus' spread."