In this Monday, March 21, 2016 file photo, officials from China's State Food and Drug Administration inspect vaccines stored at the local Center for Disease Control and Prevention office in Rong'an county in southwestern China's Guangxi Zhuang Autonomous Region. China's national prosecuting office said Friday, May 20, 2016 that 135 people in 22 provinces have been arrested for illegally buying and selling vaccines, in one of the latest scandals that has shaken the public confidence in the safety of vaccines. (Chinatopix via AP, File)

China has arrested 135 people in 22 provinces for illegally buying and selling vaccines, in the latest scandal shaking the Chinese public's confidence in vaccine safety.

In an online statement Friday, the national prosecuting office said arrest warrants were issued for 125 for running businesses without license.

It said 15 of them have been formally indicted, and two were found guilty. Ten health officials were arrested for on-duty negligence.

The accused had worked at local public health centers and knowingly bought the illegal vaccines and used them on people, the prosecuting office said.

The massive investigation followed a case in March when a doctor in the eastern province of Shandong were found to have sold 2 million doses of improperly stored or expired vaccines. Media reports said she stored the vaccines at room temperature, instead of keeping them refrigerated as required.

Vaccines not stored and managed properly can lose their effectiveness and may not protect people being inoculated. The vaccines in the March case included those for hepatitis B, rabies, mumps and Japanese encephalitis.

The scandal drew criticism from people upset with persistent food and drug safety issues in the country. Beijing quickly ordered an investigation to crack down on illegal businesses of vaccines.

  • In this Monday, Nov. 16, 2009 file photo, a health worker prepares a dose of H1N1 vaccine at the start of a free vaccination program intended for all Beijing residents at a clinic in Beijing. China's national prosecuting office said Friday, May 20, 2016 that 135 people in 22 provinces have been arrested for illegally buying and selling vaccines, in one of the latest scandals that has shaken the public confidence in the safety of vaccines. (AP Photo/Ng Han Guan, File)

  • In this Monday, March 21, 2016 file photo, officials from China's State Food and Drug Administration inspect vaccines stored at the local Center for Disease Control and Prevention office in Rong'an county in southwestern China's Guangxi Zhuang Autonomous Region. China's national prosecuting office said Friday, May 20, 2016 that 135 people in 22 provinces have been arrested for illegally buying and selling vaccines, in one of the latest scandals that has shaken the public confidence in the safety of vaccines. (Chinatopix via AP, File)

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