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

The 2007 US approval for use of live attenuated influenza vaccine (LAIV) in children aged 24-59 months included precautions against use in (1) children <24 months and children aged 24-59 months with (2) asthma, (3) recurrent wheezing, and (4) altered immunocompetence. A postmarketing commitment was initiated to monitor LAIV use and the frequency of select safety outcomes in these cohorts. Vaccination rates and the frequency of hospitalizations or emergency department visits within 42 days after LAIV and trivalent inactivated influenza vaccine (TIV) administration were estimated from 2007 to 2009 claims data from a health insurance database. Rates of LAIV use per 10,000 child-days among cohorts 1, 2, and 4 were low relative to rates among the LAIV-recommended population (2007-2008; 0.03-0.78 vs. 1.32, 2008-2009; 0.08-3.26 vs. 5.94). However, rates of LAIV use per 10,000 child-days in cohort 3 were similar to rates among the LAIV-recommended population (2007-2008; 1.55 vs. 1.32, 2008-2009; 5.01 vs. 5.94). The rate of emergency department visits/hospitalizations within 42 days of vaccination with LAIV was the same as or less than the rate within 42 days of vaccination with TIV. Less restricted LAIV use in children with past wheezing may be related to the broad definition of recurrent wheezing used in national guidelines and the current study. In the small number of nonrecommended children receiving LAIV, no safety signals were identified.