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Vaccination will work better than culling, say bird flu experts

Control strategy changes tack, now H5N1 virus is endemic


The mass culling of poultry to contain outbreaks of avian flu is no longer acceptable and should be replaced by the vaccination of flocks. That was the conclusion of experts at a joint conference in Paris of the UN Food and Agriculture Organization (FAO) and the World Organisation for Animal Health (OIE).

So far, culling has been the method of choice for controlling outbreaks. Vaccines exist, but the problem has been distinguishing infected birds from vaccinated ones, as both groups carry antibodies to the virus. This means that infected but otherwise healthy, vaccinated birds could provide a haven in which the virus can mutate undetected, increasing the risk of a pandemic strain that causes disease in humans. Trade in vaccinated birds is also subject to bans.

Last year, the OIE and FAO urged that vaccination be considered alongside other control methods. But they have now gone much further, stating that mass culling as the main means of control is no longer acceptable, “for ethical, ecological and economic reasons”.

“This is a massive change in policy,” says Robert Webster, director of the World Health Organization's Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds.

The shift was driven by a realization that the lethal H5N1 strain is widespread in wild and domestic bird populations, such as ducks. This means that no matter how often affected poultry flocks are culled, the virus is likely to reappear. Methods have also been developed to distinguish infected from uninfected vaccinated birds, either using unvaccinated ‘sentinel’ birds kept within vaccinated flocks, or vaccines that elicit slightly different antibodies from the natural virus, so that a molecular test can tell the two apart (see Nature 427, 573; 2004).

Webster says he is encouraged that the OIE and FAO accept “the reality that H5N1 in Asia is now endemic, and the possibility that more countries will have to turn to vaccination in the longer term”.

Experts at the Paris meeting, held on 7–8 April, acknowledged that many countries do not have the resources for a vaccination programme, so they are calling for $100 million–120 million in aid over three to five years for this purpose. So far, only Germany, Japan and the Netherlands have pledged support for affected Asian countries.


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Butler, D. Vaccination will work better than culling, say bird flu experts. Nature 434, 810 (2005).

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