- The Washington Times - Monday, November 28, 2005


As China and Vietnam vaccinate millions of chickens in an effort to stamp out a worrisome strain of bird flu, a question emerges — can immunized birds still silently spread infection?

Scientists in the Netherlands put the question to a test, using vaccines against a strain different from today’s H5N1, and concluded that vaccinating poultry can block viral spread among birds.

“Vaccination can be an attractive tool to prevent outbreaks of highly pathogenic [avian influenza] viruses in poultry, thereby achieving the aim of eliminating the source of human infections,” concluded lead researcher J.A. van der Groot of the Netherlands’ Central Institute for Animal Disease Control.

Birds catch numerous strains of influenza, but only a few types are particularly deadly to both fowl and people. Today, the H5N1 strain is the worst. At least 68 persons have died from H5N1 in Asia since 2003, almost all linked to contact with sick birds, and millions of birds have died or been slaughtered in an effort to contain the virus.

Health experts fear that the bird flu one day could mutate into a virus easily passed from person to person; but, so far, there is no evidence of that occurring.

Mr. van der Groot and colleagues tested two vaccines against the H7N7 bird-flu strain by housing infected chickens together with healthy, vaccinated ones.

Two weeks after inoculation, both vaccines completely blocked the spread of H7N7 among chickens, they reported yesterday.

Some transmission occurred one week after vaccination, but the virus reproduction rate already had dropped enough that the researchers predicted only a small number of new infections.

There were marginal differences in effectiveness between the two vaccines, however, leading the researchers to conclude that poultry vaccines’ ability to stop viral spread should be tested before health authorities choose which one to use.

The research backs guidelines from the United Nations’ Food and Agriculture Organization, which recommends targeted vaccination of poultry as one measure to control outbreaks of bird flu.

So far, the H5N1 virus has not been found in U.S. birds. If a bird outbreak did occur here, the Agriculture Department has stockpiled poultry vaccine to be used to help contain it.

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