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

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