In the nondescript central Chinese city of Heze, in Shandong province, Pang Hongwei had run a lucrative sideline in a thriving black market for vaccines. Its exposure last year shook China’s immunisation system to its foundations.

A pharmacist at the Peony People’s Hospital, and known to her clients as Auntie Pang, she achieved sales worth Rmb4.8m (about $700,000) through her side-business, before being caught and sentenced in 2009 to three and a half years in jail. Ms Pang’s sentence was suspended, however, and no time was served.

Instead, in 2011 she registered as a sales employee at a pharmaceutical company, moving to the provincial capital of Jinan where she began buying close-to-expiry vaccines from manufacturers and selling them to medical clinics — enrolling her 21-year-old daughter, a medical graduate, in the scheme.