The federal government has developed a human vaccine against the H5N1 bird flu, but it is only moderately effective, hard to make, and probably not protective against emerging strains of the fearsome virus.
The new vaccine, produced by Sanofi Pasteur in Swiftwater, Pa., under a $150 million government contract, is "a small step" toward being prepared for a possible global flu epidemic, said Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, which funded the vaccine research.
A study of the vaccine published in today's New England Journal of Medicine found that it stimulated a meaningful immune response only about half the time -- and only in healthy adults given two high doses over 28 days. In contrast, a single low-dose seasonal flu shot is 75 percent to 90 percent effective.
This low potency, coupled with the fact the vaccine is grown in chicken eggs -- the same problematic technology used to make seasonal flu vaccine -- means that barely 1 percent of the world's population could be immunized even if worldwide production were ramped up.
"This isn't going to be the vaccine that's going to protect us," said Gregory A. Poland, a Mayo Clinic infectious disease and vaccine researcher who wrote an editorial that accompanies the study.
Despite the vaccine's limitations, U.S. health officials are going ahead with plans to stockpile enough to immunize about 4 million people, Fauci said during a news conference this week.
That would cover high-priority groups -- notably health care providers and vaccine plant workers -- and provide "a very tenuous stopgap" if a pandemic hits soon, Fauci said.
The H5N1 virus has decimated bird flocks in Central Asia, Eastern Europe and Africa over the past year. So far, it has not mutated into a flu that can spread easily from person to person, even though almost a decade has passed since it first jumped from chickens and killed seven people in Hong Kong.
If the virus becomes contagious among people, experts say the impact would be calamitous. Humans have no natural immunity against H5N1 -- of the 176 confirmed human cases in seven countries, more than half have died -- and the ever-changing virus has shown resistance to anti-viral drugs.
Scientists are racing to create vaccines, and at least 30 promising drugs are in the pipeline, including some that would make cumbersome egg-based production obsolete.
But the race involves many obstacles and controversies, as the new vaccine shows.