Emerging data on the safety and efficacy of influenza vaccines in children.

Conventional trivalent inactivated influenza vaccine (TIV) has limited efficacy in young children, particularly those who are immunologically naive at the time of vaccination. Intranasally administered live attenuated influenza vaccine (LAIV) offers several advantages over TIV. LAIV is more convenient to administer and has shown superior protective efficacy in children as compared with TIV. A pivotal multicenter efficacy trial in 6- to 59-month-old children revealed that the relative efficacy of LAIV versus TIV against culture-confirmed influenza-like illness was 55%. This study also showed increased wheezing in 1-2% of LAIV-treated infants <24 months of age with a history of wheezing/asthma between days 10 and 28 postvaccination. Infants 6-11 months of age had an increased rate of hospitalization overall (3.5% increase) and hospitalization due to respiratory cause (2% increase). LAIV should be considered, for reasons of efficacy, the preferred influenza vaccine for children. However, safety concerns will limit its use in children <24 months of age. An alternative method for improving efficacy of influenza vaccination might be the use of adjuvanted injectable vaccine. A pilot study with MF59 adjuvanted vaccine has shown it to offer superior immunogenicity over conventional TIV, and further studies are in progress.We are living through an active period of influenza vaccine development. The threat of an influenza pandemic has resulted in increased influenza research in general and promoted development of seasonal influenza vaccines for children. This article will focus mainly on the efficacy of live attenuated intranasal influenza vaccine as an option in young children.