Officials insist laboratory leak ‘extremely unlikely’ and deny response has lacked transparency.
Provinces across China have imposed tougher restrictions in an effort to contain the country’s worst coronavirus outbreak in months, with health officials attributing the surge in COVID-19 infections to the highly contagious Delta variant.
Authorities reported 328 symptomatic infections in July – almost equal to the total number of local cases from February to June.
“The main strain circulating at present is the Delta variant … which poses an even greater challenge to virus prevention and control work,” Mi Feng, spokesman for the National Health Commission (NHC), said at a news briefing on Saturday.
It came a day after the World Health Organization (WHO) urged governments globally to contain Delta before it turns into something deadlier and draws out the pandemic.
The WHO said an 80-percent average increase in COVID-19 cases was recorded over the past four weeks in five of the health agency’s six regions, a jump largely fuelled by the fast-spreading Delta variant.
First detected in India, the strain has now reached 132 countries and territories.
“Delta is a warning: it’s a warning that the virus is evolving but it is also a call to action that we need to move now before more dangerous variants emerge,” the WHO’s emergencies director Michael Ryan told a news conference.
According to a leaked document by the US Centers for Disease Control and Prevention, a review of findings from other countries showed that while the original SARS-CoV-2 was as contagious as the common cold, each person with Delta infects on average eight others, making it as transmissible as chickenpox but still less than measles.
In China, the current outbreak is geographically the largest to hit the country in several months, challenging its early success in curbing the pandemic.
More than 260 infections nationwide have been linked to a cluster in Nanjing city, in the eastern province of Jiangsu, where nine cabin cleaners at an international airport tested positive on July 20.
Hundreds of thousands have already been locked down in the province, while Nanjing has tested all 9.2 million residents twice.
The contagiousness of the Delta variant, combined with the peak tourist season and high passenger circulation at the airport, has led to the rapid spread of this outbreak, NHC official He Qinghua told reporters at the briefing.
Fresh cases reported on Saturday in two more regions – Fujian province and the sprawling megacity of Chongqing – included one patient who visited the tourist city of Xi’an, in Shaanxi province, and an international cargo crew member who recently travelled from overseas, authorities said.
Officials in one Chongqing district ordered emergency mass testing late on Friday for people who had visited venues linked to confirmed cases.
After one asymptomatic case was discovered in Zhengzhou – the epicentre of recent deadly floods in central Henan province – city officials on Saturday ordered mass testing of all 10 million residents. The head of the city health commission was sacked.
Hunan’s tourist city of Zhangjiajie, whose landscape inspired the Avatar blockbuster, locked down all 1.5 million residents and shut all tourist attractions on Friday, according to an official notice.
Health officials said the virus was likely brought there via the Nanjing cluster, according to preliminary investigations.
Officials are now scrambling to track people nationwide who recently travelled from Nanjing or Zhangjiajie, and have urged tourists not to travel to areas where cases have been found.
After reports that some people sickened in the latest cluster were vaccinated, health officials said this was “normal” and stressed the importance of vaccination alongside strict measures.
“The COVID vaccine’s protection against the Delta variant may have somewhat declined, but the current vaccine still has a good preventative and protective effect against the Delta variant,” said Feng Zijian, virologist at the Chinese Center for Disease Control and Prevention.
More than 1.6 billion vaccine doses have so far been administered nationwide as of Friday, the NHC said. It does not provide figures on how many people have been fully vaccinated.
Health officials have said they are aiming for 80 percent of the population to be fully vaccinated by yearend.