[In summary: Worldwide influenza activity from 20 May to 22 Sep 2012 was elevated in the temperate Southern Hemisphere and tropical regions compared with their levels outside the usual influenza season.
In the United States, low levels of seasonal influenza activity were detected, and influenza A (H3N2) viruses were most commonly identified. Antigenic characterization of viral isolates from specimens submitted during the summer demonstrated that the majority of influenza A viruses are antigenically similar to the influenza vaccine strains contained in the current Northern Hemisphere 2012-13 vaccine available for us this season.
More than 300 cases of the influenza A (H3N2) variant virus were detected in 10 states but not elsewhere. The majority of these cases were associated with direct contact with swine.
The majority of recent influenza A viruses are well-matched to the influenza vaccine for this season.
Annual influenza vaccination remains the best method for preventing influenza and its associated complications, but the 2012-13 seasonal influenza vaccine does not provide protection against the H3N2v virus. Although community transmission of this H3N2v has not been identified, the potential for this virus to develop the ability to transmit efficiently from person-to-person is of concern. Rapid and intensive investigation of each variant case is necessary to evaluate the spread of disease and the possibility of person-to-person transmission.
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