The share price of Guangzhou Baiyunshan Pharmaceutical Holdings dropped by more than 9 percent on both Shanghai and Hong Kong exchanges Monday, after its latest clinical report made experts doubt the effectiveness of the Hepatitis B vaccine that the company has been working on.

According to the report, published Friday, the occurrences of adverse events in experiment and placebo groups were both over 12 percent, meaning that no serious adverse event occurred.

Some pharmaceutical industry experts said that the results of the experiment are not satisfactory because they indicate that the vaccine was not very effective, Beijing-based newspaper Economic Information Daily reported Monday.

However, the newspaper also cited other experts saying that the vaccine produced by Baiyunshan is more effective than other companies' products.

China's Hepatitis B vaccine market has been plagued with scandals in recent years.

Two infants died and another was in critical condition in Central China's Hunan Province after receiving injections of Hepatitis B vaccine produced by Shenzhen-based Biokangtai Co, Xinhua reported Friday.

Hunan's branch of the China Food and Drug Administration suspended the use of the two lines of Hepatitis B vaccines produced by the company, and initiated a probe into the reasons for the infants' death, Xinhua reported.

Biokangtai said it produced its vaccines in accordance with China's Good Manufacturing Practice for Drugs and inspected its products to ensure their high quality, according to a statement on Monday.

In mid-2011, Shanghai-listed Chongqing Brewery Co, which had worked on Hepatitis B vaccines for more than a decade, announced that its research had failed, leading to its share prices later dropping more than the daily limit for 10 trading days.