Beijing, China --- A coronavirus cluster that emerged in the Chinese city of Nanjing has now reached five provinces and Beijing, forcing lockdowns on hundreds of thousands of people as authorities scramble to stamp out the worst outbreak in months.
China has previously boasted of its success in snuffing out the pandemic within its borders after imposing the world's first virus lockdown in early 2020 as COVID-19 seeped out of Wuhan in the center of the country.
But an outbreak this month driven by the fast-spreading Delta variant has thrown that record into jeopardy since it broke out at Nanjing airport in eastern Jiangsu province.
The city reported a total of 184 local coronavirus cases Friday after nine cleaners at Nanjing Lukou International Airport tested positive on July 20.
At least 206 infections nationwide have been linked to the Nanjing cluster, which officials have confirmed as the highly transmissible Delta variant.
"It was discovered that these cleaners took part in cleaning the cabin of flight CA910" from Russia on July 10, said Nanjing health official Ding Jie.
Hundreds of thousands have been locked down in Jiangsu province, of which Nanjing is the capital, while the city has tested all 9.2 million residents twice.
In Beijing's Changping district, where two locally transmitted cases have been found, 41,000 people in nine housing communities were placed under lockdown Thursday, according to city officials.
The infections are the first local cases reported in the capital in six months.
The outbreak is geographically the largest in several months, challenging China's aggressive containment efforts which have relied on mass testing, lockdowns and swift contact tracing.
China's top disciplinary watchdog has blamed Nanjing airport officials for "poor supervision and unprofessional management" including not separating cleaning staff who worked on international flights from those on domestic flights.
Most of the early Nanjing patients had been vaccinated, a senior doctor in the city was quoted as saying by local media last week, leading online users to question the efficacy of domestic vaccines.
"If the goal is to slow down the spread and reduce the fatality rate, can afford a certain degree of protection," top Shanghai infectious disease expert Zhang Wenhong said in a social media post Thursday.
"But as for the goal of eradicating the virus, it may be something that the current vaccine cannot achieve."
The tourist city of Zhangjiajie in Hunan province has become another focal point of the latest outbreak after at least 18 cases were traced to the city, including infections picked up at a theatre, reported the state tabloid Global Times.