Optimizing Protection against Influenza for VFC-Eligible Children

Background: Children eligible for the Vaccines for Children (VFC) Program are immunized against influenza at lower rates than insured children and are also less likely to receive their second recommended dose.  Children immunized with either 1 or 2 doses of live, attenuated influenza vaccine  (LAIV) are protected against influenza better than children comparably immunized with trivalent, inactivated influenza vaccine (TIV).

Objectives: To compare the aggregate immunity produced in a model VFC population using only LAIV compared with a TIV only strategy.

Methods: Published estimates of vaccine efficacy (VE) and vaccine utilization data from a nationwide study of randomly selected pediatric practices were used to calculate the percentage of children that would be protected following immunization.

Results: 22,329 doses of influenza vaccine were administered to 20,626 VFC-eligible children aged 24 months to 17 years in the study population.  Of children recommended to receive 2 doses of influenza vaccine, only 1234 of 3018 (41%) 24-59 month olds and 469 of 1908 (25%) 5 to 8 year-olds received their second dose.   73-83% of the vaccinated VFC population would be immune if immunized with LAIV compared with 53-68% with TIV.  Differences in aggregate immunity were greatest among 24-59 month olds where 71-78% of LAIV immunized children were immune compared with 48-60% for TIV.   In this model, 29-47% more children aged 24-59 months would be immune prior to peak influenza season when vaccinated with LAIV. 

Conclusions: Because VE is higher - especially for partially immunized children - and most VFC children fail to receive their second recommended dose, a substantially greater proportion of the population is protected when immunized with LAIV.  While LAIV cannot be given to all children, LAIV should be used preferentially for the VFC population, particularly for children aged 24-59 months and those needing 2 doses.