A US postmarketing evaluation of the frequency and safety of live attenuated influenza vaccine use in nonrecommended children younger than 5 years: 2009-2010 season

The 2007 US approval for use of Ann Arbor strain live attenuated influenza vaccine (LAIV) in children aged 24 through 59 months included precautions against use in (1) children <24 months and children aged 24 through 59 months with (2) asthma, (3) recurrent wheezing, and (4) altered immunocompetence. Results from the third season (2009-2010) of a 3-year study postmarketing commitment to monitor LAIV vaccination rates and frequency of hospitalizations or emergency department visits within 42 days after LAIV are reported here. As in the first 2 seasons, LAIV usage in cohorts 1, 2, and 4 were low relative to those in LAIV-recommended populations. The only numerically increased risk observed was for respiratory events in children aged <24 months administered LAIV, compared to those administered trivalent inactivated influence vaccine (TIV). The number of children vaccinated with LAIV was small and precluded precise quantification of rare event