BOAO, Hainan -?A senior Chinese drug regulator stressed strict measures to fix the loopholes in the country's vaccine distribution system on Wednesday.

Shandong police announced last month that they had arrested a mother and daughter suspected of illegally selling improperly stored or expired vaccines worth more than 570 million yuan (88 million U.S. dollars), involving 20 provincial-level regions since 2011.

The scandal has revealed problems in the distribution of vaccines, said Wu Zhen, deputy head of China Food and Drug Administration (CFDA), while attending the Boao Forum for Asia in south China's Hainan province.

The CFDA is working with law enforcement authorities to thoroughly investigate the scandal and ensure the safety of vaccines, Wu said.

Wu vowed to identify and fix loopholes, severely punish wrongdoers and publicize information in a timely manner. Vaccines are generally well-managed in China through rules for distribution and use, he added.

The China Food and Drug Administration said Tuesday that it has given local authorities until Friday to find out who bought the mishandled vaccines.

Police in East China's Shandong province have detained 37 suspects implicated in the vaccine case. Three pharmaceutical companies are being investigated.

Police in Hunan, Jiangxi and Guangdong provinces also have reported detaining suspects over the scandal.

Although produced by licensed manufacturers, the quality of the vaccines is questionable as they had not been transported or stored properly.

This year's Boao Forum for Asia started on Tuesday. The four-day conference is themed "Asia's New Future: New Dynamics and New Vision."