A task force established by the Chinese government has pledged thorough investigation into and stern punishment of those involved in a scandal in which millions of dollars' worth of improperly stored vaccines were sold to patients nationwide.

The cross-departmental working group, led by Bi Jingquan, head of the China Food and Drug Administration, convened its first plenary session Tuesday to set the tone for the investigation.

The group was set up Monday and headed to Shandong Province the same evening.

Anyone who tries to conceal facts or provide fake information to hinder the investigation will be harshly punished, the task force said at Tuesday's meeting, adding the scandal has exposed long-standing loopholes in the vaccine distribution system.

Officials found guilty of negligence should be held accountable, said the group, which consists of officials from departments such as the National Health and Family Planning Commission, the Ministry of Public Security, the Ministry of Supervision, and the Supreme People's Procuratorate.

The working group said progress of the investigation, including scientific assessment of the effectiveness of and risks posed by the vaccines used in the case, will be released in a timely manner, in response to public anxiety.

Preliminary investigation showed that improperly stored vaccines worth 310 million yuan (48 million U.S. dollars) have been sold in more than 20 provinces since 2011.

Twenty-nine pharmaceutical companies have been implicated in selling the vaccines, and 16 vaccination institutions are suspected of buying them.

More than 130 people have been questioned and 69 criminal cases have been filed nationwide.

Dr. Lance Rodewald of WHO China's immunization program said China's public vaccination system is fundamentally sound, but warned that regulation of private-sector vaccines should be tightened.

In the latest scandal, the vaccines involved are categorized by China as voluntary immunizations rather than those required for all children.

The World Health Organization expert said the expired vaccines do not pose a threat to children who have received them, adding they will not have a toxic effect, although some children may need to be revaccinated.