China has an ongoing outbreak of delta variant. Last I heard it was up to 300 positive cases in over a dozen provinces. It is believed that a Russian flight crew member deposited virus in a plane. Two of the Nanjing cleaning crew caught the virus and spread it locally. By the time this was identified, the virus had escaped Nanjing.
China has been very vigilant about what are called here import cases. Primarily at airports but also along borders, some of which can be fairly porous and loosely regulated in far flung regions. Back last fall there were two family members who became sick and tested positive in SH. Traced back to the airport. So the entire block was quarantined for 2+ weeks, blocked off with safety tape, while workers in hazmat suits interacted with them and disinfected. The medical personnel and guards and others involved were not permitted to return home, with temporary housing for them built on site on the cordoned-off street. Much contact tracing and lots of testing undertaken to help contain that minor outbreak.
2 cases unchecked can become 200, then 2000, then 2 million.
Which is why the new outbreak is so alarming. 300 cases is a big number, spread across roughly 15 disparate locations. Hard to contain and contact trace. One infected person had gone to a 3000 seat theater in a different town on vacation. It's also the more transmissible Delta variant.
So China is very concerned this could get out of hand.
Which could require a month long national lockdown, which no one wants.
Another issue is China only has roughly a 50% vaccination rate. Partly because the Chinese vaccines are reported to be only 50% - 72% effective, while the risk of contracting the virus is quite low. While CH pharmaceutical companies have had plenty of scandals over the past 2 decades, so institutional trust is low.
I assume many of the officials being sacked are at the airport and involved in Nanjing health protection and planning, failing to protect citizens from imported airplane-related cases.