China on Thursday (Jul 29) reported small COVID-19 outbreaks driven by the Delta variant in three provinces as a cluster linked to an eastern airport spreads despite mass testing and a vaccination drive.

The flare-up, which began after nine workers at the Nanjing airport tested positive on Jul 20, has since seen 171 cases detected in Jiangsu province, while infections have spread to at least four other provinces.

It is geographically the largest spread for several months, challenging China’s aggressive containment efforts which have relied on mass testing, lockdowns and swift contact tracing.

The virus first emerged in the central city of Wuhan, but China has extolled its success in largely extinguishing the pandemic inside its borders, allowing the economy to rebound.

The new outbreak, coupled with cases seeping over the porous border with Myanmar, is threatening that record.