How did the Hohhot epidemic come about?

The epidemic in Hohhot began on September 28th, and the first case was a nurse in a hospital. The infected strain belongs to the evolutionary branch of Omicron mutant BF.7, and several reasons are summarized: First, the virus sequenced as the evolutionary branch of Omicron mutant BF.7 is the third subtype derived from Omicron mutant BA.5, which has strong toxicity, rapid spread and easy cross-infection. Second: Hohhot is the capital of Inner Mongolia Autonomous Region, with dense population, great mobility and frequent traffic. Third: the weather is getting cold, and this climate is easy to cause the spread of the epidemic. Fourth: There were few epidemics before Hohhot, so people's awareness of epidemic prevention would be weak.