Questions surround China bird flu vaccine

(Aug 31, 2006) China is working on a bird flu vaccine for humans and initial test results suggest it is safe and effective, but a leading expert is treating the news with caution, saying more details and independent checks are needed.

Government-backed Beijing Sinovac Biotech Co. said this week it had developed a H5N1 vaccine for humans, using a strain of the virus that had been found in recent years in Vietnam.

In the first clinical trial that ended in June, 120 volunteers were injected with the experimental vaccine and none showed "serious adverse reactions". Their blood and urine showed the vaccine was safe for human use, Sinovac said in a statement.

Four different dosages of the vaccine were used, but the one with 10 micrograms appeared to be most effective, stimulating 78.3 percent of protective antibodies. The company gave no other details on the vaccines.

But an expert greeted the news with caution and asked if independent laboratories had carried out tests for antibodies. "

Lots of tests are needed to evaluate the effectiveness of any experimental vaccine," said microbiologist Guan Yi at the University of Hong Kong, who has studied the virus since it made its first known jump to humans in Hong Kong in 1997. "

Vaccines made elsewhere have to be tested and verified by dozens of independent laboratories at every stage. This is the acceptable standard," he said.

The Chinese vaccine was jointly developed by the Chinese Centers for Disease Control and Prevention and supported by China's Ministry of Science and Technology.

Pharmaceutical companies around the world are trying to develop a vaccine for the H5N1 virus, which experts fear could mutate into a form that can pass easily among humans, possibly killing millions. For the moment, the virus remains essentially a disease in birds.

Flu viruses mutate constantly and experts fear that any pre-pandemic vaccine that is designed now might not confer enough protection against the eventual pandemic strain, if it emerges.


Questions surround the positive test results from China.

"How many of the participants developed antibodies?" Guan asked.

He questioned the rationale for using the Vietnam strain as a basis for the vaccine because different strains are circulating in Indonesia, northern China, Europe, the Middle East and Africa.

"This strain is different from the one in Indonesia and new ones that have emerged in other places," Guan said, calling for a more systematic and mature criteria on selecting the vaccine strain and the manufacturing process.

"The vaccine could bring a small reaction for other H5N1 strains, it won't be completely ineffective. But when you create a vaccine, you try to make one that confers the most widespread protection, but the coverage of this one is narrow," he said.

Sinovac, meanwhile, has plans to refurbish and expand its existing plant for seasonal flu vaccine to produce up to 20 million doses a year of pandemic flu vaccine from 2007. (from Reuters)


Useful links