The head of the World Health Organization has said it will be years until bird flu is eliminated in poultry, and that until then the world must remain vigilant against a human pandemic of the disease.

W.H.O. Director-General Margaret Chan told the organization's executive board Monday that countries have made heroic efforts to eliminate the deadly H5N1 strain of the virus when it has arisen in poultry flocks, but it has come back again and again.

The H5N1 strain emerged in 2003. There have been 267 confirmed cases of bird flu in humans since then, mostly in East Asia, and 161 people have died from the disease. More of those deaths occurred in 2006 than in the previous years combined.

Chan also said the U.N. agency must address a wide range of other health issues, including malaria, measles, polio and nutritional deficiencies.

Chan made the comments in her first address to the executive board as director general. She took office on January third after serving as an assistant director general in charge of infectuous diseases.

Previously, Chan managed outbreaks of avian flu and of the SARS virus as Director of Health in Hong Kong.