A medical worker gives a polio vaccine to a child in Hami prefecture in Northwest China's Xinjiang Uygur autonomous region in an undated photo. [Cai Zengle / for China Daily]

The Shandong food and drug watchdog issued a public notice Saturday evening on hundreds of clues and identities linking 300 suspects to illegal deals of vaccine sales in 24 provinces, municipalities and autonomous regions.

Police have busted 21 cases in Inner Mongolia, Henan, Hebei and Shandong and arrested six suspects implicated in the sales of problematic vaccines.

Among those arrested are a mother surnamed Pang and her daughter, who were charged for illegal vaccine sales worth more than 570 million yuan ($88 million) in at least 24 provincial-level regions.

The case is the largest of its kind in China in terms of the amount of money involved.

Since 2010, the suspects purchased 25 types of vaccines from more than 100 pharmaceutical salesmen, both licensed and unlicensed and were sold to illegal agents or even local disease control and prevention centers at high prices, according to Jinan Public Security Bureau in Shandong province.

Of the 300 suspects made public by the food and drug watchdog, 107 allegedly supplied the mother-daughter pair with the vaccines and 193 were suspected of buying vaccines from them.

The China Food and Drug Administration urged all suspects to turn themselves in and reveal the whereabouts of the vaccines. It also called on local food and drug departments to work with the police during the investigation.

It is against the law in China to sell vaccines without proper licenses.

Though produced by qualified manufacturers, the quality of the vaccines was questionable as they were not transported in approved conditions. Such vaccines have potential side-effects and can even cause disability or death if they become expired.

The case has been transferred to the procurators.