Newly born babies receive vaccines at a hospital in China.Reuters

A vaccine scandal in China began building slowly and then suddenly, this weekend, it was everywhere at once.

The story began back in November, when a large vaccine manufacturer called Changsheng Biotechnology Co. was forced to recall 252,600 ineffective doses of vaccines for DPT (diphtheria, pertussis, and tetanus). Then earlier this July, a government investigation caught Changsheng falsifying data about its rabies vaccine, and a local food and drug administration fined the company 3.44 million yuan, or approximately $500,000, over the faulty DPT vaccines.

Over the weekend, an anonymous post recounting all this and more went viral on the Chinese social network WeChat. In addition to the recent developments, it alleged a complex web of corruption that went back decades, involving other vaccines for hepatitis B and chicken pox. The post was deleted the next day.

But by then, a full-blown national scandal had erupted. The Chinese government this week scrambled to put out statements assuring a prompt investigation. President Xi Jinping described the situation as “vile and shocking.” Police on Monday announced the swift arrest of four of the company’s executives, including its chairwoman.

Changsheng’s vaccines have not yet been tied to any deaths or illnesses, but the story caught on because it so perfectly echoed many scandals that have rocked China in recent years. In 2016, for example, a hospital pharmacist sold two million doses of vaccines improperly stored in an “overheated, dilapidated storeroom.” That came after scandals over tainted milk, infant formula, pork, cooking oil, and water. The scandals, one after another, have undermined trust in the government’s ability to keep the public safe.

“People in leadership aren’t doing their best by the people,” one user commented on Weibo, a Twitter-like Chinese social network. “It’s a series of scandals about fake baby formula, fake vaccines, child abuse in daycares, sexual assault ... everything we eat, wear, and use endangers us.”

“My children already drink imported baby formula, now they need to start getting imported vaccines,” said another Weibo user. “Might as well leave the country for all our health needs.” Since 2008, when formula tainted with the chemical melamine killed six babies and sickened 300,000 more, Chinese parents have been wary of domestic formula. Those who can go to Hong Kong to buy infant formula. And since news of the faulty vaccines broke, clinics in Hong Kong have been fielding calls from panicked parents in mainland China. One Hong Kong clinic told the South China Morning Post that its phone had been ringing nonstop.

By Tuesday, Weibo users had viewed hashtags related to the vaccine scandal more than 600 million times, according to The Guardian. A Weibo post from the state-run newspaper People’s Daily urged calm over the matter. “Don’t spread panic and anger. Relevant departments must respond in a timely manner with updates,” read the headline.

The now-deleted WeChat post—which still lives on in parts of the internet, such as on the Ethereum blockchain—was not restrained. In a conspiratorial tone, it spins a long, complicated tale of shareholders, eye-popping profits, mistresses, and more. At times, the language is unflinchingly direct: “Experts at the Peking University Health Science Center summarized the act of injecting the ineffective vaccines in people in one word: murder.” And it made the story viscerally relevant to readers: “The vaccines they produce are flowing every day into you and your child’s bodies.”

WeChat is ubiquitous in Chinese life, and it has become a major and decentralized source of news in China. (The app is essentially a messaging app, but it has features of Facebook, iMessage, Instagram, Venmo and Skype all rolled into one.) Columbia Journalism Review recently highlighted how the platform has enabled the rise of independent writers untethered to legacy media outlets. But it has also enabled a type of news that thrives on social media. “Heavy on emotion and light on accuracy, the most-read and shared stories on the WeChat platform are often selective with details,” writes Mia Shuang Li in CJR. Hoaxes such as stories about foods causing cancer flourish on the platform. Fake news on WeChat is such a problem that fact-checking sites have also sprung up.

One section of the now-deleted WeChat post recounts the death of several babies after hepatitis B vaccinations in 2013. Those widely publicized deaths set off a panic of their own. A subsequent government investigation published in The International Journal of Epidemiology concluded that the babies died of unrelated causes—and that one other baby suffered an allergic shock from the vaccine but recovered. “The timeliness of the investigation and its communication may have played an important role in regaining confidence and use of hepatitis B vaccine,” the study’s authors concluded.

The anonymous WeChat post in fact mentions that the investigation cleared the vaccine—and also mentions that it was government investigators who cleared it. For readers in China, trust in the investigation only goes as far as their trust in the government that conducted it.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.