New-style bird flu vaccine shows promise

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The vaccine against H5N1 avian influenza, made by Baxter International, is the first bird flu vaccine to be made using cells in a lab dish instead of chicken eggs. This is important because the right type of chicken eggs are difficult to obtain - and because H5N1 kills chickens rapidly.

The trial of more than 250 people was a phase I/II safety trial, but the report, published in the New England Journal of Medicine, showed the vaccine produced a strong immune response in people who received two doses.

Adding an immune system booster called an adjuvant did not make the vaccine work any better, Dr. Hartmut Ehrlich, vice president of global research and development for Baxter's BioScience business and colleagues, found. This was puzzling as adjuvants have helped other bird flu vaccines,

The H5N1 avian flu virus has become firmly entrenched among birds in much of Asia and parts of Europe, Africa and the Middle East. It rarely infects people but it has killed 241 people in 15 countries, according to the World Health Organization.

Experts fear the constantly mutating virus could change into a form easily transmitted from person to person, perhaps sweeping the world and killing millions.

At least 16 companies are working on vaccines against H5N1. No one knows if they will work against whatever strain might eventually cause a pandemic, but makers agree it is better to be prepared.

One serious hold up had been the use of fertilized chicken eggs, which are used to produce all influenza vaccines.

"Embryonated eggs are available only seasonally, which creates a time constraint in the manufacturing of yearly vaccine and certainly could influence preparedness for a pandemic," Dr. Peter Wright of Vanderbilt University Medical Center wrote in a commentary.

Cell-based vaccines would require less advance planning and could be made year-round, he said.

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