The risk of an influenza pandemic is not likely to decrease in the future, according to a report released Thursday by the World Health Organization.

Currently, the greatest threat for a possible pandemic comes from the H5N1 form of the avian flu virus. The report said additional complications resulting from the new forms of the virus are “now circulating in different parts of the world.”

Since appearing in Hong Kong in 1997, the H5N1 strain of avian flu has affected 256 people worldwide and killed 152. It devastated much of Southeast Asia’s poultry population and continues to spread.

“The global picture of influenza viruses in the avian world has changed significantly since 2002,” the report said. “The massive die-off of migratory birds at Qinghai Lake in mid-2005 was unprecedented, and migratory birds now appear to be contributing to geographical spread of highly pathogenic virus.”

The report is important for many reasons, said Marguerite Pappaioanou, a University epidemiology professor. It noted the economic dependence many of the countries with infected birds have on poultry, she said.

The public-health world needs to understand that farmers’ livelihood and national economies depend on this poultry, Pappaioanou said.

“That’s good protein,” she said. “Those working in animal health must find new ways to fight the virus without devastating those people and economies.”

The report stressed the need to monitor viral resistance to antiviral drugs.

Because of the genetic diversity in different forms of influenza, researchers are struggling to develop a vaccine.

“To date, results from clinical trials of candidate pandemic vaccines have not been promising, as these vaccines confer little protection across the different genetic groups,” the report said.

A separate WHO report issued in October said the world is on course for a massive vaccine shortage.

“We are presently several billion doses short of the amount of pandemic influenza vaccine we would need to protect the global population,” Dr. Marie-Paule Kieny, director of WHO Initiative for Vaccine Research, said in the October report. “This situation could lead to a public health crisis.”

As the virus continues to evolve in humans and animals, the report stressed the need for a field test to quickly diagnose the H5N1 virus.

Researchers also said more needs to be done to contain the virus in animals, including culling and vaccinating infected birds.

Just this week, Egypt reported its seventh death from the H5N1 virus. The 39-year-old woman most likely contracted the virus from infected ducks she defeathered and slaughtered. Her death raises this year’s toll to 74 people, up from 42 deaths last year.

The extensive spread of the virus to poultry is linked to waterfowl, namely ducks and geese, rather than chickens.

“Recently, studies have demonstrated that the virus is now moving both ways in relay transmission, from poultry to migratory birds and back again,” the report said. “This finding might help explain some of the continuing geographical spread.”