New observational data from the U.S. Flu Vaccine Effectiveness Network and two additional studies conducted during the 2013-’14 influenza season unexpectedly showed that the live attenuated influenza vaccine (LAIV) was not effective against the influenza A H1N1 pandemic strain (H1N1 pdm09) virus when compared with inactivated influenza vaccine (IIV) in children 2 through 8 years of age. In particular, children 2 through 8 years immunized with LAIV were not protected against H1N1 pdm09.

The data were presented at the Oct. 29 meeting of the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention (CDC).

Estimates of vaccine effectiveness during the 2011-’12 and 2012-’13 influenza seasons suggested that LAIV effectiveness was similar, but not superior to IIV against influenza A H3N2 and influenza B viruses. These findings are contrary to earlier studies that had suggested superior efficacy of LAIV in children ages 2 years through 8 years....

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