WASHINGTON—Confused about what to do about the bird-flu threat? Wonder whether you should get Tamiflu or wait for a vaccine? Here are some basic questions and answers drawn from government agencies and research scientists:
Q. What's the difference between Tamiflu and a vaccine against bird flu?
A. Tamiflu—scientific name oseltamivir—is an antiviral drug that's designed to treat the seasonal flu virus that kills about 36,000 Americans every year. Tamiflu doesn't prevent the flu, but it reduces the severity and duration of the disease. It disrupts the virus' ability to reproduce in the body, and it increases the likelihood that a patient will survive. To be fully effective, it must be taken in the first 48 hours after symptoms appear. The drug's effect lasts only as long as you're taking it.
A flu vaccine, on the other hand, is designed to keep the virus from entering cells in your body in the first place and from spreading to other cells and perhaps infecting other people. Unlike an antiviral drug, a vaccine's protection lasts for months.
"There's not much we can do to contain the flu if we don't have a vaccine," said Tara O'Toole, the director of the Center for Biosecurity at the University of Pittsburgh Medical Center.
Q. Will Tamiflu help against the dangerous H5N1 flu virus that's already killed 64 people in Asia?
A. Scientists aren't sure. It may help keep already sick people from dying, and it might limit the spread of the disease from a small, local outbreak. But it's not likely to prevent a mass infection. "There is no clinical evidence that it (Tamiflu) will work" against H5N1, said Daniel Perez, a bird-flu expert at the University of Maryland, College Park. "But we still have to have it."
Q. How does Tamiflu work?
A. It keeps the virus from spreading by interfering with the action of a knob-shaped protein—a bundle of organic molecules labeled NA—on the surface of the virus. The NA protein is responsible for letting newly formed viruses escape from an infected cell. Tamiflu doesn't prevent the initial infection.
Q. Is there enough Tamiflu to go around?
A. No. By the end of November, the government will have stockpiled 4.26 million "treatment courses" of Tamiflu. A typical treatment course consists of 10 doses of the drug taken over five days. The government intends to build a stockpile of 20 million treatment courses—200 million doses—next year. That's enough for fewer than 7 out of every 100 Americans. At first, the drug is supposed to be limited to health-care and emergency workers and especially susceptible people.
The sole manufacturer of Tamiflu, the Swiss company Roche Pharmaceuticals, can produce 55 million treatment courses a year. Roche says it will make 150 million courses in 2006 and 300 million in 2007, which is still less than 5 percent of the world's population. Roche is considering licensing others to make more of the drug.
Q. Should I lay in a personal supply of Tamiflu?
A. No. The Department of Health and Human Services has warned against personally stockpiling Tamiflu and has asked providers not to prescribe the drug as a preventive against a pandemic. Hoarding Tamiflu would worsen the already severe shortage of the drug.
"Healthy people who keep packs of Tamiflu in the bureau drawer might be denying immediately needed treatment to those most vulnerable to severe complications related to the seasonal flu," said Richard Harkness, a pharmacist in Ocean Springs, Miss.
Q. Are there other antiviral drugs?
A. Three others: zanamivir (known as Relenza), amantadine and rimantadine. They're older than Tamiflu and not as effective, since the seasonal flu viruses are developing resistance to them.
Q. Does the standard vaccine for routine seasonal flu help with bird flu?
A. No. Regular flu shots don't protect against the H5N1 virus because they were designed for different strains of human flu. But the government advises that you get the usual flu shot anyway for your general good health.
BIRD FLU AND VACCINES:
Q. How do seasonal flu vaccines work?
A. Both kinds of seasonal flu vaccines—a shot in the arm or a nasal spray—cause your immune system to produce billions of tiny particles called antibodies. These antibodies make it impossible for the virus to enter your cells and they keep the virus from spreading to infect other cells or people. Unfortunately, these antibodies don't work against H5N1.
Q. What's the difference between bird flu and human flu?
A. All flu viruses originated in birds. Many types of flu viruses infect birds, but only a few infect humans. Each type is named for the particular combination of two proteins, labeled HA and NA, on the surface of the virus that enable it to cause disease. The HA protein governs the virus's ability to enter a host cell and multiply. The NA protein controls the release of newly formed virus from the host to infect others.
All combinations of HA and NA proteins occur in birds, but only three combinations commonly afflict humans. They are H1N1, which caused the 1918 Spanish Flu pandemic; H2N2, the cause of a 1957 virus; and H3N2, the source of a 1968 epidemic. This year's seasonal flu vaccine protects against the H1N1 and the H3N2 virus. The H2N2 virus no longer is circulating.
The new, very aggressive H5N1 combination has killed millions of birds and 64 humans in Asia in the last two years, and has spread to Eastern Europe. The fear is that H5N1 could adapt itself to pass easily from person to person, setting off a pandemic.
Q. How do people catch bird flu?
A. So far, people are catching the H5N1 virus from close contact with infected birds, such as children playing around chickens. In one case, an infected child apparently spread the disease to her mother and aunt; all three died. The great concern is that the virus will change into a form that spreads easily among people.
Q. How could the bird flu virus change so it can pass easily from person to person?
A. In either of two ways. First, small random genetic changes are always accumulating in a virus, a process known as genetic drift. This is what happened in 1918. Secondly, a person who's carrying a human flu virus could be infected by the H5N1 virus and swap some of their genes, as happened in 1957 and 1968. This process, called reassortment or genetic shift, could produce a human version of H5N1.
"People simultaneously infected with human and avian influenza strains could become a mixing bowl for the disease," says a statement from the National Institute of Allergy and Infectious Diseases in Bethesda, Md.
Q. Why is the H5N1 virus so dangerous?
A. It's a new virus for humans, so no one has natural immunity. As yet there's no proven vaccine. In addition, H5N1 is extremely lethal, killing more than 50 percent of the humans it's infected. Scientists have spotted a mutation that increases the size of the HA protein, allowing it to enter cells more easily. They also have discovered that the H5N1 virus triggers 10 times as many inflammatory proteins, which cause pneumonia and other respiratory problems, as seasonal flu.
Robert Webster, a leading vaccine expert at St. Jude Children's Hospital in Memphis, calls it "the strongest virus we have ever seen." If a pandemic begins, it is "virtually unstoppable," O'Toole said.
Q. Will there be a vaccine against the H5N1 virus?
A. Webster's group developed an experimental vaccine in 2003. It's being tested in 450 children and adults, and hasn't yet been approved for public use. However, the government has ordered $162 million worth of the vaccine, enough to treat 20 million people, to be stockpiled as a precaution. Unfortunately, that much vaccine won't be available until 2010.
Q. Will the experimental vaccine work if the H5N1 virus changes so that it can pass easily between people?
A. Scientists aren't sure how effective it will be against a different form of the virus. "It's mostly a way to contain the spread of the disease," said Perez of the University of Maryland, who's a member of the team that developed the vaccine. "It's better than nothing."
"If a distinct H5N1 virus should suddenly emerge, an additional new vaccine against that strain may be needed," said the statement from the National Institute of Allergy and Infectious Diseases. It then would take at least six months to produce an effective new vaccine.
Q. Will there be enough vaccine?
A. At present, vaccine manufacturers produce enough vaccine to protect only 300 million people—5 percent of the world's population—against seasonal flu.
Drug makers told the World Health Organization that they might be able to produce enough for 1.7 billion treatment courses—28 percent of the world's population—against the H5N1 virus by 2008.
Q. How are large quantities of vaccine made?
A. Samples of flu virus are injected into millions of hens' eggs, where they multiply. Later the virus is extracted, purified and modified so it can't cause illness. The egg-based process can take 10 months and can't be adapted swiftly to a new strain of virus.
President Bush has requested $2.8 billion to develop another, faster way to make vaccine, in large vats of kidney cells that have been infected with the flu virus. This technology works in weeks instead of months.
Q. Has the H5N1 virus reached the United States?
A. No, but it could do so at any time in wild birds or infected poultry products. The most likely route would be an infected airline passenger entering from affected areas in Asia, Perez said.
For more information online, go to www.pandemicflu.gov, the official U.S. government Web site for information on pandemic flu and avian influenza.
(c) 2005, Knight Ridder/Tribune Information Services.
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