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Cold, Flu, & Cough Health Center

2009-10 Influenza (Flu) Season

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    Yes, antibodies made in response to vaccination with one flu virus can provide protection against related viruses. This can result in reduced vaccine effectiveness against the related viruses, but it can still provide enough protection to prevent or lessen illness severity and prevent flu-related complications. (However, a flu vaccine is not expected to offer cross-protection against viruses that are very different genetically from those in the vaccine.) In addition, it's important to remember that the seasonal flu vaccine contains three viruses so that even when there is a less than ideal match or lower effectiveness against one virus, the vaccine may protect against the other two viruses. For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend seasonal flu vaccination. This is particularly important for people at high risk for serious flu complications and for their close contacts.

    Will the seasonal vaccine protect against the new H1N1 virus?

    The seasonal vaccine is not expected to protect against the 2009 H1N1 virus because it is very different genetically from the seasonal H1N1 virus that is in this season's vaccine. That is why the government and manufacturers are producing a separate 2009 H1N1 vaccine designed to protect against the 2009 H1N1 virus.

    What is CDC doing to monitor seasonal flu vaccine effectiveness for the 2009-10 season?

    CDC carries out and collaborates with outside partners to assess the effectiveness of seasonal flu vaccines. During the 2009-10 season, CDC is planning multiple studies on the effectiveness of the seasonal influenza vaccine and the 2009 H1N1 vaccine. These studies will measure vaccine effectiveness in preventing laboratory-confirmed seasonal and 2009 H1N1 influenza infections in children, pregnant women, health care workers, and adults.

    What is CDC doing to monitor antiviral resistance in the United States during the 2009-10 season?

    Antiviral resistance means that a virus has changed in such a way that antiviral drugs are less effective in treating or preventing illnesses caused by the virus. Samples of viruses collected from around the United States and worldwide are studied to determine if they are resistant to any of the four FDA-approved influenza antiviral drugs.

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