Last year, it sold 252,600 substandard DPT vaccines to inoculate children against diphtheria, whooping cough and tetanus, a regulator in the northeastern Jilin said on Friday. The shot is covered by China's immunisation plan and is mandatory for children.
Years later, nearly half of Chinese food-processing plants still failed to meet internationally acceptable standards, according to a 2015 report. The Dpt vaccine is given to newborn babies across the country.
However, response from the public intensified.
The company behind the rabies vaccine, Changchun Changsheng Biotechnology, has faced criticism after the China Food and Drug Administration (CFDA) revealed that the company had violated good manufacturing practice (GMP).
The scandal first emerged a week ago, when it was found that the company's anti-rabies vaccines were faulty and didn't meet immunity standards.
It is rare for the Chinese president to comment on a domestic issue while overseas, and this reflects the government's urgency to control the damage - especially on the credibility of China's health system - caused by the latest medical scandal.
In the statement Sunday, Li promised to "resolutely crack down" on violations that endanger public safety.
Jilin province, where the company is based, said Tuesday it also would open a corruption investigation into government officials involved. Those who have committed criminal offences would be handed over to the public security department.
Changsheng has apologised, saying that it was "guilty and embarrassed" and would co-operate with drug regulators to carry out a comprehensive internal investigation.
The fact that the main villain is a private company and not a government agency part explains why the scandal has been covered in the Chinese press, escaping the type of heavy internet censorship other issues often attract.
For their mistake, Changsheng was fined 3,442,887 yuan ($507,843) by the Chinese government.
While reactions to the Changsheng scandal were initially censored, it appears that Chinese censors have now been forced into being more lenient as the scandal has become the only piece of news that anyone in China seems to be talking about, with frequent updates and many threads on Weibo containing hundreds, if not thousands, of critical comments.
After a brief trading halt, shares of Changchun Changsheng's parent company also fell by the 10 per cent limit.
China is hit regularly by quality-control scandals, fuelling fear over the safety of food and medicines and anger at regulatory lapses.
Separately, authorities in Hebei province near Beijing announced on Monday that almost 150,000 people had received a substandard diphtheria, tetanus and pertussis vaccine made by another firm, Wuhan Institute of Biological Products.
But inevitably questions will be asked about the role of the public watchdog - the Food and Drug Administration (FDA) - in all of this, as well as why an investigation was reportedly launched into the company in October, but vaccines not pulled until this month. Immunoprophylaxis concerns diphtheria, pertussis and tetanus (Dpt).