A team of government investigators has been sent to Biokangtai, a drug maker based in the southern city of Shenzhen, state broadcaster China Central Television said, amid growing public concern about the safety of its products.
The probe was launched after provincial and health authorities separately reported that since November, around a half-dozen babies died shortly after they received hepatitis B vaccines made by Biokangtai. One case has been ruled out while the others were still being investigated.
"Coincidental diseases arise the most easily and are the easiest to misinterpret," the statement on Biokangtai's website said.
A senior government expert in diseases said vaccine-related deaths could be due to coincidence, but that Biokangtai was not in the position to make an objective assessment.
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The vaccines were being given to children free of charge as part of the government's national immunisation program. But Chinese health authorities suspended the use of Biokangtai's hepatitis B vaccines last Friday after the first deaths of babies were reported.
Four babies reportedly died in the southern province of Guangdong, although one of them was said to have died from pneumonia. The National Health and Family Planning Commission reported that two babies in Hunan province and another in Sichuan had also died in a similar way.