WASHINGTON -- A British drug manufacturer announced yesterday that it has developed what appears to be the most effective bird flu vaccine so far and that it can be made in sufficient quantities for widespread distribution in case of an outbreak.
The experimental vaccine, manufactured by GlaxoSmithKline PLC, seems to work at low enough doses that it overcomes a key obstacle in earlier vaccines, which required high doses and would have been too cumbersome to produce rapidly in large quantities.
"It's really taking us a quantum leap forward in terms of the feasibility of making a vaccine for people who need it in the case of an outbreak," said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.
The company will soon start talking with regulators in the United States and Europe about getting permission to sell the vaccine, and it could begin producing the active ingredient, or antigen, by the end of the year, a spokeswoman said.
The first documented cases of people infected with the H5N1 bird flu virus occurred in Hong Kong in 1997, and infected birds have carried the disease to Africa and Europe. According to the World Health Organization, 232 people have been infected, 134 fatally, most recently a 17-year-old from Thailand who died Monday.
So far, the virus has not mutated into a form that can easily spread among people. But some scientists, saying it's only a matter of time before the next worldwide human flu pandemic, believe such a mutation is likely.
There are a limited number of plants for making vaccines, however, and the manufacturing process typically relies on an old, egg-based procedure that takes time.
For months, pharmaceutical companies have had trouble creating a vaccine that not only would be effective but also would work at low-enough doses that the few manufacturing facilities available to make the vaccine could produce enough of it.
Preliminary tests indicate that GlaxoSmithKline has developed just such a vaccine. It uses a second ingredient, called an adjuvant, to boost the impact of the active ingredient without requiring a larger dose.
"We expect to have the antigen as something we'll produce this year, and then we'll work with governments to see what they want or need," said Patricia R. Seif, a company spokeswoman. She said shipping could start in January.
Glaxo's experimental vaccine must still undergo further testing - to see, for example, whether it works safely and effectively in children. In the United States, the Food and Drug Administration would have to approve its sale.
Given the nature of vaccines, Jeffrey Levi, executive director of the advocacy group Trust for America's Health, said the additional testing could be expected to yield similarly positive test results. The FDA has pledged to rapidly review promising vaccines.
The preliminary tests were conducted on 400 adults ages 18 to 60, who were vaccinated twice. Results showed that more than 80 percent of the test subjects had a strong immune response. The dose was just 3.8 micrograms.
By comparison, tests on a vaccine developed by Sanofi Pasteur, based in France, indicated that its vaccine worked a little more than half the time at a dose of 90 micrograms, according to a study published in March. That vaccine lacked a booster.
Thirty-microgram doses of a Sanofi vaccine candidate with an adjuvant worked in two-thirds of cases, according to separate test results, which were released in May.
Health specialists say the major remaining obstacle is making sure the Glaxo vaccine works on whatever form the virus would take, if and when an outbreak occurred.
The vaccine's active ingredient is based on a form of the virus that would probably have changed if the virus started passing from human to human, according to the health experts.
"If it's mutated significantly, then the vaccine may not be effective," Levi said. If the vaccine can be adjusted to work well against a mutated virus, he said, the shots could be produced quickly to help during an outbreak.
Additional testing should determine by the end of the year whether the vaccine would protect people from a mutated virus, said Seif, the Glaxo spokeswoman.
She expected the company would formally request approval from regulators by the end of the year. The company would be able to produce the booster ingredient whenever regulators granted approval.
Thai authorities told the WHO that the teenager who died Monday developed symptoms several days after burying dead birds.
In the worst-case scenario, the Bush administration says as many as 2 million Americans could die during an outbreak.