Flu activity is low in most of the United States, but a wave of influenza B virus activity is affecting parts of the country. It's possible that significant flu activity could continue into May. CDC still recommends that people get a flu vaccine if they have not yet this season. And remember that flu antiviral drugs are a second line of defense to treat flu illness. People at high risk of serious flu illness should call a health care provider if they get flu symptoms.

What You Should Know for the 2013-2014 Season

Antigenic Characterization

The image shows the different features on an influenza virus, including the surface proteins (hemagglutinin and neuraminidase) against which antibodies are formed after influenza infection or vaccination.

CDC antigenically characterizes about 2,000 influenza viruses every year to compare how similar currently circulating influenza viruses are to those that were included in the influenza vaccine, and to monitor for changes in circulating influenza viruses. Antigenic characterizationcan give an indication of the flu vaccine’s ability to produce an immune response against the influenza viruses circulating in people.

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