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Imperfect Vaccine May Be Best Option For Bird Flu

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  • Imperfect Vaccine May Be Best Option For Bird Flu

    POSTED: 5:02 pm EDT April 3, 2006

    WASHINGTON -- The most effective way to combat an outbreak of bird flu in people would require a rapid and aggressive vaccination campaign as soon as the outbreak began, even if the vaccine wasn't a perfect match, a study concludes.

    Flu viruses are constantly changing, and a vaccine aimed at a specific strain can't be developed until scientists identify the form infecting humans. That's why the annual human flu shots must be updated every year.

    But even a bird flu vaccine that is poorly matched to the form that breaks out would be likely to provide some protection and could help slow the spread of the disease, according to a research team headed by Timothy C. Germann of Los Alamos National Laboratory.

    In addition to the vaccine campaign, the researchers said rapid use of several million doses of antiviral medicines such as Tamiflu could help stem an outbreak.

    Their findings, developed by using computer models of how flu spread would be affected by vaccines, other medication and social steps such as closing schools and restricting travel, are published in this week's online edition of Proceedings of the National Academy of Sciences.

    The outbreak of H5N1 bird flu in Asia has now spread to Europe and scientists are concerned that it could become a worldwide pandemic if the virus changes in ways that enable it to spread easily from person to person.

    More than 100 people have died from the virus, but most seem to have contracted the disease from domestic or wild fowl, with the illness slow to spread from one human to another.

    If it develops that person-to-person ability and is not quickly contained at its source, "international travel could carry pandemic viruses around the globe within weeks to months ... causing a worldwide public health emergency," Germann's team warned.

    Indeed, just last week Dr. Anthony Fauci, the government's leading bird-flu scientist, said he was more worried about the virus arriving in a sick airline passenger than via migrating birds.

    A vaccine for the bird flu is currently under development and early tests indicate it is effective in about 50 percent of patients, though it requires a much larger dose than the regular annual flu shot. To date, the stockpile is enough for 4 million people with a goal of being able to protect at least 20 million people.

    Targeting antiviral drugs to people in the area of flu cases is likely to be effective only during the earliest stages of an outbreak due to the labor-intensive requirements. As the flu spreads a community health system could be overwhelmed by the number of cases, the researchers said.

    Because of the importance of children in transmitting the flu, school closures are likely in an effort to reduce exposure to the virus and either legal or voluntary travel restrictions could also occur, the study said.

    However, the research team reported, their study indicated that even a 90 percent reduction in domestic travel would slow the spread of the flu by only a few days to weeks and would not reduce the eventual size of the outbreak.

    While the vaccine under development requires two doses to be effective, the researchers said the most effective response to an outbreak would be a rapid effort to deliver single doses as rapidly as possible, getting partial protection, possibly supplemented with antiviral drugs.

    The spread of flu could potentially be controlled by delivery of 10 million doses of vaccine per week for 25 weeks, they concluded.

    In a separate paper also being published online by PNAS researchers said that combining air travel and commercial shipping data with climate information could help indicate areas at risk of epidemics caused by the spread of disease-carrying mosquitoes.

    In the report, Andrew Tatem of England's University of Oxford and colleagues analyzed more than 30,000 international ship and aircraft routes. They found the spread of the Asian tiger mosquito -- which has not been linked to disease -- followed high-traffic sea shipping routes.

    "The next major advancement in the health of American people will be determined by what the individual is willing to do for himself"-- John Knowles, Former President of the Rockefeller Foundation

  • #2
    ??? imperfect vaccines can limit illness to 10% ???

    Travel bans won't stop bird flu: study

    By Maggie Fox, Health and Science Correspondent

    Travel restrictions and school closures will do little to stop a pandemic of bird flu from marching across the United States, but they may slow it enough to distribute drugs and vaccines, according to a new study published on Monday.

    "It's probably not going to be practical to contain a potential pandemic by merely trying to limit contact between people such as by travel restrictions, quarantine or even closing schools," said Timothy Germann of Los Alamos National Laboratory in New Mexico, who worked on the report.

    "But we find that these measures are useful in buying time to produce and distribute sufficient quantities of vaccine and antiviral drugs."

    Their study, published in the Proceedings of the National Academy of Sciences, supports the approach being pursued by the U.S. government and recommended by the World Health Organization for preparing for a possible influenza pandemic.
    "Our model suggests that the rapid production and distribution of vaccines, even if poorly matched to circulating strains, could significantly slow disease spread and limit the number ill to less than 10 percent of the population, particularly if children are preferentially vaccinated," the team at the U.S. Department of Energy's Los Alamos National Laboratory and the University of Washington wrote.

    Catherine Macken of Los Alamos said the computer model used in the study provided a surprising finding -- using a weak vaccine in many people would be better than trying to vaccinate a smaller number of people with a more effective dose.
    "If you reduce somewhat the length of time that someone is infective ... you end up getting a significant impact," Macken said in a telephone interview.

    "You might be better off vaccinating twice as many people, getting a lower level of protection, but still getting an improvement in susceptibility."

    No flu vaccine is perfect and experts have been uncertain which approach would work better.

    Using several million doses of drugs like Roche AG's Tamiflu and GlaxoSmithKline's Relenza that can help prevent influenza infection could also help, the researchers said.

    The H5N1 strain of avian influenza is spreading rapidly in birds around the world and experts believe it will soon be found everywhere. It rarely infects people, but has sickened 190 people and killed 107 of them, according to WHO.
    If the virus mutates slightly and gains the ability to pass from person to person easily, it is likely to become much less fatal but could cause a pandemic.

    Scientists are racing to make a vaccine against it and governments are trying to stockpile drugs that can prevent and treat the infection, but supplies are low.

    In the meantime, health experts are trying to work out the best way to deal with a pandemic if it comes, and want to know if schools, businesses and transportation should be closed to try to slow the flu's spread.

    The team at Los Alamos and the University of Washington ran a complex computer simulation of what the spread of bird flu might look like in the United States. They say their findings would hold for any highly mobile society.

    "In the event that a pandemic influenza virus does reach the U.S., according to our results, the U.S. population could begin to experience a nation-wide pandemic within 1 month of the earliest introductions," the researchers wrote.

    The model assumes that about a third of the population would become infected -- the rate seen in the past two pandemics, in 1957 and 1968. They included several circumstances for people to meet and potentially pass the virus along, including households, neighborhoods, preschools, playgroups, schools, shops and work.

    I sure hope that computer model is programmed accurately, since we may be staking our lives on it.

    "The next major advancement in the health of American people will be determined by what the individual is willing to do for himself"-- John Knowles, Former President of the Rockefeller Foundation