WANG SHENGSHENG, a lawyer who lives in Guangzhou in southern China, is the mother of a newborn baby. The province’s health officials advised her, she says, to have her baby vaccinated not only against tuberculosis and hepatitis-B (which is mandatory) but also against chickenpox, hepatitis-A, meningitis and other diseases, which is not. She did so, and got a hepatitis-A vaccination herself. A few days later, China’s latest medical scandal erupted. The country, it turns out, has been using millions of doses of outdated or improperly stored vaccines for the diseases not covered by the mandatory programme.

Ms Wang did not take this lying down. Shocked by the lack of information about the health implications of receiving faulty vaccines, and concerned that she may have unknowingly endangered her child, she joined 12 other lawyers in writing an open letter to the national government demanding a national investigation and full disclosure into what is fast becoming China’s worst medical scandal since 2008. That year, America’s Food and Drug Administration found that a Chinese manufacturer had been adulterating heparin, an anti-blood-clotting drug. There was also a huge public outcry in China that year when it was revealed that more than 300,000 children had fallen ill and six had died after drinking tainted milk.

The vaccine scandal first came to light a year ago when police in Shandong, an eastern province, arrested a pharmacist and her daughter. Allegedly, they had been buying vaccines that were out of date or about to expire and selling them to hospitals and clinics across the country. “We found the storage space to be a mess,” one of the policemen said. “There were no proper refrigeration facilities.”

At first, the government’s reaction was sluggish to non-existent. The story did not come to widespread notice until March, when a website called The Paper began looking into the case, and the police finally made public what had been going on. Many users of social media denounced the authorities for the scandal and for their slow reaction. China Daily, a state-owned newspaper, said officials had no one to blame except themselves. The open letter from the lawyers in Guangzhou demanded the government check all its records so people could find out whether they had been vaccinated with an out-of-date batch. It also asked who would bear the cost of re-vaccination and what would be done for anyone harmed as a result of receiving the dodgy vaccines.

In all, roughly 2m faulty vaccines are thought to have been sold, for a total of 570m yuan ($90m). The scandal has implicated 29 pharmaceutical firms and 16 health departments. The police are pursuing 69 criminal cases. On March 28th the government finally launched its own investigation under the China Food and Drug Administration. The prime minister, Li Keqiang, said the case had “exposed many regulatory loopholes”.

China has a two-tier vaccination system. Mandatory vaccines, such as those against hepatitis-B, are provided free by provincial disease-control authorities, which are responsible for production and distribution. Non-mandatory vaccines, such as for chickenpox, have to be paid for. With the intention of bringing down the prices and improving efficiency, private companies have been allowed to compete in vaccine production, wholesale distribution and retail sales.

That has worked badly. Provincial health bureaus are poorly financed; cash-strapped disease-control departments have turned the vaccination system into a revenue stream. An anonymous public-health official in Shandong recently described to Caixin, a Chinese magazine, how the system works. The provincial disease-control centres abuse their regulatory powers to control prices and sales of vaccines. They establish fixed markups for vaccines leaving the factory, of between 10% and 25%. They dictate which hospital or clinic gets which batch, at what price. Bidding for vaccines is rare; corruption less so. “The disease-control centres”, said the official, “can use their monopoly over the vaccine market to seek profits.”

Such behaviour has been going on a long time. In 2006 the director of the immunology department of the Shandong Disease Control and Prevention Centre was sentenced to life in prison for taking bribes from vaccine producers. President Xi Jinping’s anti-corruption drive was supposed to be tackling and reducing this sort of thing. Clearly it has some way to go.

China also has supervisory bodies to sound the alert in cases of health problems. A system set up in 2006 and expanded in 2009 is supposed to provide early warning of public-health emergencies. There is also one for monitoring the quality of vaccines. Evidently neither worked properly.

The outdated vaccines do not seem to be dangerous in themselves; no deaths have been reported as a result of receiving them. The World Health Organisation describes the health risks as “very low”.

But the scandal may still have damaging consequences because anxious parents are now reluctant to have their children vaccinated. Community health workers and doctors in Guangzhou, Ms Wang’s hometown, say they have been getting dozens of calls from worried parents. Many have been going to Hong Kong and Macau instead, hoping to get vaccinated there. Indeed, so many have done so that the health authorities in those semi-autonomous territories have restricted the number of non-local children who can get vaccinated.

In other parts of China, clinics that were once usually full are now almost empty. A doctor told Sohu Health, a website: “We have been calling people telling them our vaccines are safe but they are still reluctant to come. They are waiting for this to blow over.” The trouble is that the corruption at the heart of the scandal will not just blow over. And meanwhile children are not being protected from serious diseases.