OPTIONS VI: Double-Barreled Vaccine for the Birds

TORONTO, June 22 -- If avian flu holds the potential for a human pandemic, one possible strategy is to vaccinate the birds.

To that end, Chinese researchers have created an avian flu vaccine that piggybacks on a well-known vaccine against Newcastle disease, another widespread illness of birds, they reported at the Options for the Control of Influenza meeting here.

The double-barreled vaccine would be easy to produce and distribute -- some 20 billion doses of the parent Newcastle vaccine are used every year in China, according to the researchers led by Hualan Chen, Ph.D., of the Harbin Veterinary Research Institute in Heilongjiang.

The notion of blocking a potential avian-based flu pandemic by vaccinating birds holds merit, said to Michael Perdue, Ph.D., of the World Health Organization in Geneva.

"Most people still think if we could have a strong vaccine in poultry, we could reduce the human risk," said Dr. Perdue, who moderated the session.

Current poultry vaccines for flu prevent much death and illness, he added, but are not completely protective against infection.

Newcastle disease is almost exclusively an avian disease. The rare human infections are mild and characterized by conjunctivitis, but the disease is often fatal in birds.

The vaccine can be administered in food, as a coarse spray, or injected.

Using reverse genetics, the Chinese researchers added the hemagglutinin antigen from an avian flu strain to the La Sota Newcastle disease vaccine. The dual vaccine was tested in eggs and day-old chicks and found to be harmless.

In a Newcastle disease challenge, the dual vaccine completely protected adult chickens both from illness and death, while all of the 10 birds that were given a saline control took ill and died, said Zejun Li, Ph.D., of the University of Wisconsin at Madison. Dr. Li presented the research in the absence of Dr. Chen, although he was not directly involved in the study.

Also, he noted, the vaccine was completely protective against two strains of avian flu and antibodies lasted up to four months at levels that were comparable to those seen immediately post-challenge.

The vaccine also may have a mammalian application, Dr. Li said. Balb/C mice were given two doses of the vaccine intraperitoneally three weeks apart and then challenged with avian flu two weeks later.

Within nine days, all control mice were dead, having first lost more than 20% of body weight. In contrast, Dr. Li said, all of the vaccinated mice gained weight after the challenge and none of them died.

The success of the vaccine in mice gives hope that it might be useful in a pandemic emergency, he noted, perhaps to protect high-risk individuals such as health care workers.

It would have to be a killed vaccine, though, said Dr. Perdue, because Newcastle disease infects humans so rarely. And its value in that form would depend on how much hemagglutinin antigen it contains -- information that is still to come, he said.

"The data that we didn't get was the antigen mass of the preparation," Dr. Perdue noted. "To be a useful human vaccine, it would have to have a significant antigen mass."