BEIJING • China's newest product safety scare burst onto the public consciousness when an obscure essay alleging corruption in the pharmaceutical industry became an Internet sensation.

The furore over alleged shady dealings by a major vaccine producer - the third crisis involving vaccines since 2010 - has shattered already fragile trust in regulators, and illustrates the rising frustrations of China's increasingly sophisticated consumers.

News that pharmaceutical company Changchun Changsheng Biotechnology had fabricated records and been forced to stop manufacturing rabies vaccines was first reported more than a week ago.

But it exploded on social media over the weekend, fuelled by a viral essay alleging decades of malfeasance by the company including the bribery of officials to allow low-quality products onto the market.

The origin and veracity of the mysterious post remain unverified, but the damage was done. Millions of angry users shared the essay and other information on product-safety problems in a rare public airing of a touchy national issue.

The China Food and Drug Administration (CFDA) last week said the problematic rabies vaccine had not left Changsheng's factory. But the firm was found to have sold 252,600 sub-standard DPT vaccines, a mandatory vaccine in China to inoculate children against diphtheria, whooping cough and tetanus, to Shandong province last year.

While there have been no known reports of people being harmed by the vaccine, Chinese regulators ordered Changsheng to halt production and recall the product.

As the pressure mounted, further revelations have emerged.

The authorities in the northern province of Hebei announced on Monday that nearly 150,000 people had received sub-standard DPT vaccines made by another firm, Wuhan Institute of Biological Products.

The problems have rekindled already deep fears over domestically made medicines and driven worried parents online to swop information on obtaining imported vaccines.

"We always say kids are the nation's future, but if we can't ensure the safety of such a future, what does the future hold for us?" asked Ms Huo Xiaoling, 37, who has a one-year-old daughter who received a vaccine made by Changsheng.

Ms Huo said she would no longer buy Chinese-made vaccines. "As Chinese, we probably should have confidence in our country, but getting hurt again and again has made us lose faith."

Children have been among the victims of the worst Chinese product scandals of the last decade.

In 2008, milk and baby formula tainted by the chemical melamine killed six infants and left tens of thousands hospitalised, rocking China's dairy sector and leading to a regulatory shake-up.

"Anything that touches on drug or food safety also involving children is just a huge hot button in China," said Mr Kent Kedl, Shanghai-based senior partner at consultancy Control Risks. "This is probably the highest-level of code red the government faces," he added.

President Xi Jinping - on a trip to Africa - on Monday called the vaccine company's actions "vile and shocking" and said the authorities should deal with the matter swiftly.

Many parents are sceptical about the government's response. As of Monday evening, a hashtag referring to the scandal had received tens of millions of views on Weibo, a popular social media platform.

One image circulating online shows a screenshot of a news item touting a promise from Premier Li Keqiang on Sunday to "resolutely crack down on all illegal and criminal acts that endanger the safety of people's lives".

Next to it is a similar statement Mr Li made after a 2016 vaccine scandal, suggesting the government has done nothing to address the problem.

Hong Kong clinics said they have seen a surge in demand for children's vaccines, indicating that mainland parents are taking their children to the city and neighbouring Macau for vaccines as has happened during previous scandals.

Changsheng's shares plunged by their daily limit of 10 per cent yesterday, extending falls that have seen the stock lose US$1.8 billion (S$2.5 billion) or more than half its value since the middle of the month.

Changsheng and its parent company, Changsheng Biotech, have been mentioned in at least 10 bribery-related cases in the past decade, according to China Judgment Online, a database that discloses court rulings, China Daily reported yesterday.

The data shows the company's staff or distributors paid kickbacks to people responsible for buying vaccines, including those working in hospitals or disease control departments, to be given priority in vaccine purchases.

The CFDA announced late on Sunday that it had ordered all production stopped at Changsheng and police have detained its chairman and four subordinates. Jilin province, where the company is based, yesterday said it also would open a corruption investigation into government officials involved.

But many jaded consumers have heard it all before. "The problem is who is doing the investigation," said one commentator on Weibo. "If you're just investigating yourself, what kind of results will come out?"

AGENCE FRANCE-PRESSE, NYTIMES, REUTERS