BEIJING, March 24 -- More than 130 people have been apprehended for suspected involvement in a vaccine scandal, and 69 criminal cases have been filed nationwide, the Ministry of Public Security (MPS) said Thursday.

It was recently revealed that a large quantity of improperly stored or expired vaccines had allegedly been sold in more than 20 provincial-level regions since 2011.

Hua Jingfeng, a senior official with the MPS, said at a multi-agency press conference that vaccines involved in the case had been sold for 310 million yuan (47.6 million U.S. dollars), rather than 570 million yuan as previously reported.

Investigators found that most of the vaccines involved had been used, with 20,000 doses seized and sealed by authorities, according to Hua.

Investigators are still tracing the flow of the vaccines, Hua added.

Twenty-nine pharmaceutical companies are suspected of involvement in selling the illegal vaccines, and 16 vaccination institutions are suspected of buying them, according to officials at the joint press conference of the MPS, China Food and Drug Administration and National Health and Family Planning Commission.