French researchers at the Sanofi Pasteur Institute say they have developed a bird flu vaccine that, so far, appears to be safe and effective in humans. But observers caution it's too soon to say whether the experimental drug would work in a flu pandemic.
The avian influenza type A virus H5N1 has decimated poultry in parts of Asia, Africa and Europe, and caused severe illness and death in humans. On Thursday, the World Health Organization (WHO) confirmed the first case of bird flu in an infant girl in Djibouti in east Africa.
Djibouti is the second country in Africa after Egypt to have confirmed human cases of the disease. Eight countries have identified H5N1 in waterfowl.
So far, there's no evidence it has spread from human to human, even though that is seen by health authorities as a distinct possibility. Public health officials say human-to-human transmission could cause the virus to mutate rapidly, leading to a pandemic that could kill millions.
Researchers at France's Sanofi Pasteur Institute say they have developed a vaccine to produce neutralizing antibodies in humans and disarm the virus in infected individuals. They say they have created six versions of the serum, all involving an inactivated, modified strain of H5N1, and gave two doses of the drug to 300 healthy volunteers over a 42-day period.
According to the results of the study, which were published in the British medical journal The Lancet all six versions raised immunity in all of the volunteers. The researchers said the best results were produced by a vaccine that combined the inactive virus with a weak booster agent known as an adjuvant. Investigators say there were few side effects.
Study lead author Melanie Saville says the response investigators are getting in the lab is about as good as that of any seasonal flu vaccine.
"And at the moment, this is the best thing that we can do," she said. "As without any circulation of a pandemic strain, we can't see how efficacious a vaccine would be."
But observers caution that it's hard to predict how well the vaccine would work during a highly aggressive, flu pandemic.
Anthony Fauci, director of the U.S. Institute of Allergy and Infectious Diseases at the National Institutes of Health, says annual flu shots work because they have been circulating, in slightly mutated form, within the human population for years. H5N1is an entirely new strain that has jumped the species barrier from water fowl to humans, and Fauci says that's left scientists unprepared.
"Which tells us we have a long way to go before we optimize our approach to influenza," he said.
In the United States, an experimental bird flu vaccine yielded somewhat disappointing results. In a study published in March, researchers described how the the compound stimulated protection in slightly over half of study participants receiving the highest doses.
But even so, observers say such moderately effective vaccines could be useful in limiting transmissibility, alleviating severe symptoms and limiting deaths from avian flu.