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Experimental Bird Flu Vaccine Falls Short

Just over half of volunteers appeared immunized, researchers report

WEDNESDAY, March 29, 2006 (HealthDay News) -- Only about half of the people who received an experimental bird flu vaccine produced antibodies indicating they were protected, researchers report.

Although the dose needed for even this modest effect was extremely high (about 12 times that of the annual flu vaccine), officials stopped just short of calling the trial a disappointment.

"We had hoped it would be better," acknowledged principal investigator Dr. John Treanor, a professor of medicine and an associate professor of microbiology and immunology at the University of Rochester Medical Center.

"Having a vaccine that would require 90 micrograms twice, in and of itself, would not and could not be the answer to where we want to be," added Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which funded the study. "It is a step forward, but it is a small step," he said.

Both Fauci and Treanor spoke at a news conference Tuesday.

The study, however, is a milestone in the quest to protect humans from avian flu, they added.

"It's important, because it points out areas we have to face," said Dr. Pascal James Imperator, chairman of the department of preventive medicine at SUNY (State University of New York) Downstate Medical Center. "The study was exceptionally well-done. It is a very well-designed study, therefore the results are very important."

In the past two years, the H5N1 strain of avian flu has infected poultry throughout Southeast Asia, Central Asia, Africa and Europe, prompting the destruction of millions of birds. So far, more than 100 people have died worldwide from H5N1 infection, which has spread via close contact with birds.

The big concern among academic and lay communities is that the virus will acquire the ability to jump easily between humans, leading to a pandemic and millions of deaths. Unlike the seasonal flu, humans have no immunity to bird flu.

To prepare for such a scenario, the U.S. government wants to stockpile small amounts of the vaccine to inoculate health-care workers and vaccine makers in a pre-pandemic phase.

"If we don't have people to continue to make that vaccine and health-care workers to take care of sick people coming in, we're going to be behind the eight ball really fast," Fauci said.

The U.S. Department of Health and Human Services (HHS) has already contracted with drug maker Sanofi Pasteur to produce $100 million worth of the avian flu vaccine being tested now.

The current study, appearing in the March 30 issue of the New England Journal of Medicine, involved 451 healthy adults aged 18 to 64 who were randomly assigned to receive the vaccine (two doses a month apart) or a placebo. Antibodies were measured in two different ways, with similar results.

More than half (54 percent) of participants who received the highest dose of vaccine (two shots of 90 micrograms each) had levels of antibodies considered protective against the virus.

The proportion of people who were protected decreased with smaller doses: only 43 percent of people who received two 45-microgram shots were protected, 22 percent of people receiving two 15-microgram shots and 9 percent of people receiving two 7.5-microgram shots. Some participants reported mild pain at the injection site.

An accompanying editorial called the response "poor to moderate at best."

And the study authors acknowledged that they don't know how much protection these individuals really have. "We won't know until people become exposed to the virus," Treanor said.

The researchers are now looking for ways to stretch the supply, including using adjuvants, which boost the immune system's response to a vaccine.

"Then you would be able to immunize more people with lower concentrations and only one dose," Imperator said. In fact, studies involving adjuvants are already underway.

The vaccine is already being stockpiled in small amounts, the amounts limited by the fact that the vaccine has to be manufactured in existing plants when they aren't busy producing the seasonal flu vaccine.

"In gaps where there is production capacity available, we will be stockpiling modest amounts," Fauci said. "Modest" right now means up to 8 million doses, or enough for 4 million people. HHS Secretary Mike Leavitt has indicated that he would like to have 20 million vaccine courses on hand.

All of this would be geared primarily toward a pre-pandemic effort. "If we do have a situation where we have a virus spreading from human to human [ie, a pandemic], we've got to get that virus, get a seed and make it as quickly as we possibly can," Fauci said.

More information

The U.S. Centers for Disease Control and Prevention can tell you more about avian flu.

SOURCES: Pascal James Imperator, M.D., chairman, department of preventive medicine, and director, Master of Public Health Program, SUNY (State University of New York) Downstate Medical Center; March 28, 2006, teleconference with John J. Treanor M.D., professor, medicine, and associate professor, microbiology and immunology, University of Rochester Medical Center, New York, and Anthony Fauci, M.D., director, National Institute of Allergy and Infectious Diseases, Bethesda, Md.; March 30, 2006, New England Journal of Medicine
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