Vaccinating Birds Might Limit Avian Flu Spread, Research Contends

But experts don't think the approach is practical in the field

MONDAY, Nov. 28, 2005 (HealthDay News) -- Mass vaccination of poultry at risk for avian flu may be effective in preventing the infection from spreading in birds, Dutch researchers report.

In chickens vaccinated against the H7N7 strain of bird flu, two different vaccines were each able to block viral transmission and prevent an outbreak two weeks after immunization, the study found.

"We could also not show infection of a contact chicken that was not protected. These vaccines really work very well against spreading," said lead author Dr. J.A. van der Goot, a researcher at the Central Institute for Animal Disease Control in Lelystad, the Netherlands.

Her team concluded that vaccinating poultry may be effective in preventing the spread of highly pathogenic avian influenza viruses.

However, the flu strain they tested is not the H5N1 strain, which is currently thought to pose a risk to humans.

The report appears in the Nov. 28 early online edition of the Proceedings of the National Academy of Sciences.

According to van der Goot, "We wanted to look at the effectiveness of vaccines against avian influenza. We wanted not only to look at the effectiveness for the individual chicken, but we wanted to look at the effect of vaccination on the transmission of the virus."

Vaccinating chickens is a good strategy for containing the bird flu in Europe, where the vaccines are good, a U.S. poultry science expert contended.

But in the United States, "the whole thing with bird flu vaccines is they are not very good," added Joseph Giambrone, a professor of poultry science at Auburn University.

"In the U.S. what we are saying is that we're so isolated and the industry is so sophisticated that if we get an outbreak, we are just going to kill the chickens, we're not going to vaccinate them," Giambrone said.

In its experiments, the Dutch team examined the effectiveness of vaccinations by housing small groups of infected and uninfected chickens together and tracking the transmission of the virus.

"Two weeks after vaccination, when the chicken is infected by the virus, they do not excrete any virus," van der Goot said.

However, she cautioned that the effectiveness of vaccinating chickens in the field is problematic. "It's a tool you can use," she said. "Of course, we've used it in an ideal situation. There is a big difference between what we do in the laboratory and what is done in the field."

Van der Goot also noted that the vaccines the researchers used are fresh, and every animal got vaccinated. "There are a small number of animals, and we take the time to do it," she said. "In the field, if you miss a few birds, you really have a problem."

Vaccinated birds can spread the virus to unvaccinated chickens for up to 10 days before the vaccine takes full effect. However, "when vaccination is used in the right way, it really stops transmission," van der Goot said.

On Nov. 15, China announced plans to vaccinate all its birds against the H5N1 flu. China estimates its current poultry stock at more than 5.2 billion birds, most of which are kept in small backyard flocks. The number of fowl raised and killed each year in China is close to 14 billion, experts say.

Because China has so many birds, Gambrone contended that "basically, what they are doing is a smokescreen."

He added, "The vaccines have to be produced one dose in one egg and there are not 14 billion pathogen-free eggs in the whole world. It would take three years to stockpile that many eggs. It's a logistical nightmare."

And despite mounting global concern that the H5N1 virus could mutate into person-to-person transmission, Giambrone also doesn't think that it presents any real danger to humans.

"They say that the H5N1 virus is deadly because it killed 68 people," Giambrone said. "But what they aren't telling you is that there are hundreds and even thousands of people that have gotten infected and haven't shown any signs. It's only a small amount of people that get sick. It's not as lethal as everybody thinks it is."

"If the virus was going to jump into people and cause a lot of disease and spread from person to person, it would have done so a long time ago," Giambrone added. "This H5 has been around for four or five years."

More information

For more on avian flu, head to the U.S. Centers for Disease Control and Prevention.

SOURCES: J.A. van der Goot, D.V.M., researcher, Central Institute for Animal Disease Control, Lelystad, the Netherlands; Joseph Giambrone, Ph.D., professor of poultry science, Auburn University, Auburn, Ala.; Nov. 28, 2005, early online edition, Proceedings of the National Academy of Sciences
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