Results from a clinical trial demonstrate that high doses of an experimental H5N1 avian influenza vaccine can induce immune responses in healthy adults. Approximately half of those volunteers who received an initial and a booster dose of the highest dosage of the vaccine tested in the trial developed levels of infection-fighting antibodies that current tests predict would neutralize the virus. The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, funded the study, published in the current issue of
The New England Journal of Medicine. Preliminary results from this trial were first disclosed late last summer.
H5N1 avian influenza viruses are of enormous concern to public health officials worldwide. The potential for a human avian flu pandemic looms large, say experts, as daily reports indicate an increasing spread of infection in bird populations in Southeast Asia, Europe, the Middle East and Africa. According to the World Health Organization, as of March 24, 2006, 186 people had been infected with avian flu viruses, and more than half of them had died.
Generally, flu viruses are easily transmitted from person to person, but so far, the H5N1 avian influenza viruses have not demonstrated this characteristic. In the worst-case scenario, if an avian flu virus became easily transmissible from person to person, it could trigger an influenza pandemic because humans have no pre-existing immunity to these viruses.
The NEJM article describes an analysis of data on the safety and immune responses to the vaccine. In general, the higher the dosage of vaccine, the greater the antibody response produced. Of the 99 people evaluated in the 90-mcg, high-dose group, 54 percent achieved a neutralizing antibody response to the vaccine at serum dilutions of 1:40 or greater, whereas only 22 percent of the 100 people evaluated who received the 15-mcg dose developed a similar response to the vaccine.
Generally, all dosages of the vaccine appeared to be well tolerated:
* Almost all reported side effects were mild
* The second dose of vaccine did not cause more local or systemic symptoms than the first
* Systemic complaints of fever, malaise, muscle aches, headaches and nausea occurred with the same frequency in all dosage groups as in the placebo group
* Lab tests did not reveal any clinically significant abnormalities
The vaccine, made from an inactivated H5N1 virus isolated in Southeast Asia in 2004, was manufactured by sanofi pasteur, Swiftwater, PA, under contract to NIAID. Because there are no manufacturers licensed in the United States to use adjuvants in inactivated influenza vaccines, NIAID’s first step was to test an H5N1 influenza vaccine made in a way that mimics the process used to make conventional flu vaccines. The clinical data collected in this study are now available to support the potential use of this vaccine should it be needed for an emerging pandemic.
Message posted by: Rashmi Nemade