China ended its final week of 2021 with its biggest tally of local coronavirus cases for any seven-day period since subduing the country’s first epidemic nearly two years ago, despite an arsenal of some of the world’s toughest COVID-19 measures.

The National Health Commission reported on Saturday 175 new community infections with confirmed clinical symptoms for December 31, bringing the total number of local symptomatic cases in mainland China in the past week to 1151.

The surge has been driven mostly by an outbreak in the northwestern industrial and tech hub of Xian, a city of 13 million.

The deepening outbreak in Xian will likely firm authorities’ resolve to curb transmissions quickly as and when cases emerge. The city, under lockdown for 10 days as of Saturday, has reported 1451 local symptomatic cases since December 9, the highest tally for any Chinese city in 2021.

While China’s case count is tiny compared to many outbreaks elsewhere in the world, forestalling major flare-ups in 2022 will be important. Beijing will be hosting the Winter Olympic Games in February, and the ruling Communist Party will hold a once-every-five-years congress, expected in the fall, where President Xi Jinping will likely secure a third term as party secretary.

The emergence of the highly transmissible Omicron variant will also drive Beijing to stick to its high vigilance against the virus. China has reported a handful of imported Omicron cases and at least one locally transmitted case.

Since August, China has tried to get any outbreak under control within about two weeks, much shorter than the four to six weeks in earlier battles against sporadic flare-ups following the initial nationwide epidemic, according to the National Health Commission.

Cities along China’s borders are at higher virus risk, either due to the presence of overland transport links or entry of infected travellers from other countries. Some were hit by Delta outbreaks that resulted in harsh travel curbs last year.

Yunnan, which shares a border with Myanmar, Laos and Vietnam, reported new local symptomatic cases on 92 out of 365 days last year, or 25 percent of the time, more often than any other province, autonomous region or municipality.

Xian lockdown

The Xian outbreak, which led to cases in other cities including Beijing, could be traced back to a flight arriving from Pakistan, but it was unclear how it spread to local communities.

Many people have been forbidden from leaving their residential compounds, but a city government official said on Friday curbs would be loosened in less risky compounds when the time was right.

Postgraduate student Li Jiaxin, 23, said nobody can leave the campus of her university. She spent New Year’s Eve with her three room mates and was unable to meet with her boyfriend and family.