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    Is the H1N1 Swine Flu Vaccine Safe?

    H1N1 Swine Flu Vaccine Safety: Hype, Myths, and Facts

    Is the 2009 H1N1 swine flu vaccine safe? continued...

    That's still not proof that no harm will come from the vaccine. Clinical trials cannot detect something bad that happens to one or two out of every 100,000 people vaccinated.

    "There could be unknown side effects. Something could happen. But we think that is highly unlikely," says infectious disease and vaccine expert Mark Mulligan, MD, executive director of the Hope Clinic of the Emory Vaccine Center in Atlanta.

    "The CDC, FDA, HHS [Health and Human Services Department], the Department of Defense, and several large HMOs with great medical records are all collaborating in enhanced surveillance for this national 2009 H1N1 vaccine campaign," Mulligan tells WebMD. "If there is a signal for a rare or late adverse event, we will identify it as early and as quickly as we can."

    Isn't the 2009 H1N1 swine flu vaccine too new to trust?

    Is the swine flu vaccine brand new? Yes and no. The 2009 H1N1 swine flu vaccine is made exactly the same way as the seasonal flu vaccine, by the same manufacturers using the same materials -- except for one shiny new piece.

    What has changed is the piece of the virus the vaccine uses to prime the immune system.

    Vaccine experts tell WebMD this change isn't all that new. Every couple of years or so, a new variant of a seasonal flu virus comes along. When that happens, a "new" vaccine is made using the relevant part of the variant virus.

    And even though the 2009 H1N1 swine flu is a genuinely new virus, it's still closely related to seasonal flu bugs. One of the vaccines in the three-in-one seasonal flu vaccine protects against seasonal H1N1 flu, which is about 75% similar to the 2009 H1N1 swine flu -- although it offers no protection against the pandemic flu.

    Last year, some 100 million people got the seasonal flu vaccine. No safety issues appeared. That's reassuring, but it's no proof that something rare and unexpected can't happen.

    There's no denying that the virus particle used in the vaccine has never been used before. No scientific calculation can rule out the chance that something unexpected might happen.

    But one can calculate that this chance will be small. And the chance that the vaccine will prevent serious illness and deaths is very, very large.

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