A team of eight medical experts sent by the Chinese Medical Association has arrived in Shanxi Province to help with the ongoing investigation of the latest vaccine scandal.

Specialists in neurology, allergic reaction, vaccine adverse reaction, immunization planning, as well as infectious and blood diseases were sent to Shanxi at the request of the provincial medical association to ensure the probe is scientific, transparent and accurate, Xinhua News Agency reported on Monday.

The Beijing-based China Economic Times reported on March 17 that improperly stored vaccines administered by the provincial Center for Disease Control and Prevention (CDC) had killed four children and sickened more than 70 others who had been vaccinated between 2006 and 2008.

"What's the point of the investigation given that it has been three years since the first adverse reactions allegedly caused by improper storage were first reported by families of the victims?" asked Cao Lingsheng, a division director of the Chinese Center for Disease Control and Prevention's immunization center.

"Vaccine samples taken then cannot provide valid test results, if there are any left for testing," he told China Daily.

He added that it will be hard, if not impossible, to collect sound proof to link or unlink the victims' deaths and illnesses to the vaccines.

Li Tiantian, a doctor at the Peking Union Medical College, agreed.

"It's not right to simply relate the deaths and injuries of nearly 100 children to vaccines they had received years ago, or to the improper storage of the vaccines," he noted.

Doctors find it hard to diagnose minor patients showing symptoms like twitching and fever, according to Li.

Children are usually sent to a hospital several days after showing the symptoms, making it hard for doctors to track the cause, let alone several years later, he said.

Besides, adverse reactions to vaccines, as scientific studies have found, tend to emerge shortly after the vaccination, he said.

The deaths mentioned in the report happened days or even months after immunization, said Li.

Most of the widely used type B encephalitis, hepatitis B and rabies vaccines in China contain dead microorganisms, which are safe and only become less effective if improperly stored, according to Cao.

However, he conceded that attenuated vaccines, which contain live microorganisms, might impact the recipient's health, if not properly refrigerated.

Loopholes in the vaccine management system in Shanxi should be detected and corrected through the investigation, he said.

The provincial government on March 22 admitted the provincial CDC and the vaccine provider, the Beijing-based Huawei Shidai Company, had violated certain rules, but assured the vaccines were safe.

The local government launched a special investigation into the scandal the same day, assisted by an eight-member group sent by the Ministry of Health and joined by experts from other provinces.

The provincial food and drug administration launched an inspection campaign on vaccine quality and safety last week.

The province's health authority ruled out any link between 15 children who died or fell ill and the vaccines provided by Huawei, according to a preliminary investigation result quoted in the Shanghai-based Oriental Morning Post last week.

However, the provincial authority has yet to confirm the report, as local officials and experts could not be reached for comment on Monday.