Tests of a new H5N1 bird-flu vaccine on humans find that the vaccine is safe to use but not very effective.
In the study published in today's New England Journal of Medicine, 451 adults were given either a placebo (inactive drug) or an H5N1 vaccine at four different concentrations. H5N1 is the strain of bird-flu virus currently killing wild birds, domestic poulty, several species of mammals, including humans, around the world. It has caused more than 100 human deaths.
After measuring the blood levels of those who received the vaccine, the researchers found that only one group showed much of an immune response, and that was the group that received a very high dose. Immunologists say the dose that worked is about 12 times more concentrated than the average flu vaccine.
Even then, not everyone in the group was protected -- only about 50 percent had antibody levels high enough to indicate immunity.
That it takes so much vaccine to induce such a small amount of immune system reaction is not good news for producing a vaccine in large quantities, but researchers remain hopeful.
The study's lead researcher, Dr. John Treanor of the University of Rochester, said his team and others are now working on ways to boost the effectiveness of the vaccine with chemicals called adjuvants, which may allow the vaccine to be used at lower doses.
Continued research in this field is vitally important, said Dr. Gregory A. Poland, a professor at the Mayo Clinic College of Medicine. He wrote an accompanying editorial that ran with the study.
"To do otherwise, with the pandemic clock ticking, could prove to be too little, too late," he said.