Bird Flu Vaccine Only Works at Highest Dose: Study

An experimental vaccine against H5N1 bird flu only appears to work at the very highest doses, meaning it will be harder than feared to protect the population against a pandemic.. The vaccine, made by a unit of Sanofi-Aventis and based on an H5N1 virus that killed a Vietnamese man in 2004, only produced a satisfactory immune response in volunteers at two doses of 90 micrograms each. That is 12 times what is needed for the annual seasonal flu shot. "It is a bit of muted good news in that we are going in the right direction, but the sobering news is we have a long way to go," National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci said in a telephone briefing before the findings appeared in the New England Journal of Medicine. These findings mean there is only enough H5N1 vaccine now in the U.S. stockpile to protect about 4 million Americans in a pandemic, Fauci said. These would likely be key health-care workers and people working to make the vaccine. Everyone else would have to wait while a pandemic spreads, relying on public-health measures such social distancing -- meaning closing businesses, schools and using masks, gloves and other protective equipment -- in the meantime. The H5N1 avian influenza virus has spread in birds at an alarming rate in recent months, sweeping out of east Asia across to Europe and down into Africa. Officials believe it will become entrenched in wild birds across the globe within a year or two. It remains difficult for humans to catch but has infected 186 people in eight countries and killed 105, according to the latest World Health Organization figures. Experts fear the virus could evolve into a form passed easily from human to human, causing a pandemic that could kill tens of millions. SQUEEZING OUT EXPERIMENTS Because influenza viruses mutate quickly, it is impossible to prepare a vaccine in advance that would precisely match a pandemic strain. And flu vaccine capacity is extremely limited because of low demand, even though seasonal influenza kills more than 250,000 people every year globally. Several companies and the U.S. National Institutes of Health are working on H5N1 vaccines, squeezing in production at corporate factories during lulls in making the annual seasonal flu vaccine. Dr. John Treanor of the University of Rochester in New York and colleagues tested Sanofi-Pasteur's experimental H5N1 vaccine on 450 volunteers. "Only the 90-microgram dose was associated with antibody responses," they wrote in their report, published in the New England journal. They said trials were underway in elderly persons, persons with impaired immunity, or children, who may have a different response. The annual flu vaccine mixes the three most common circulating strains of flu at 15 micrograms each. A pandemic vaccine would probably only use one strain. But with two 90-microgram doses needed to produce a satisfying immune response, current manufacturing capacity falls far short, Fauci and Treanor said. Most people only need a single dose of seasonal flu vaccine. Global capacity for making influenza vaccines is 900 million doses. The United States would need vaccine to protect 300 million people, but the most companies have ever made for the U.S. market is 83 million doses. Fauci said the hope is that U.S. suppliers including Sanofi, Chiron Corp., GlaxoSmithKline and MedImmune will make 120 million doses of seasonal flu vaccine this year. GETTING UP TO SPEED "It is going to take quite a while to get that type of vaccine-manufacturing capacity up to scale," Fauci said. More than 30 trials of an H5N1 vaccine are underway, many of which look at ways to stretch the vaccine by lowering the dose and adding other drugs to boost the immune response and lower the actual vaccine dose needed. Some are also looking at faster and more modern production methods. Dr. Gregory Poland of the Mayo Clinic in Rochester, Minnesota noted the antibody response measured in the study does not always protect people from sickness with flu, but rather lowers the risk of death and serious complications. He said work also is underway to make a vaccine against a second substrain of H5NI that has started to kill people. "Source":[ http://today.reuters.com/news/NewsArticle.aspx?type=healthNews&storyID=uri:2006-03-30T133407Z_01_N28219992_RTRUKOC_0_US-BIRDFLU-VACCINE.xml&pageNumber=0&summit=].

---

Related articles

Scientists find bird flu antibody - Antibodies that could protect against bird flu in humans have been isolated by an international team of scientists (30.5.2007)