Current status of live attenuated influenza vaccine in the United States for seasonal and pandemic influenza

A live attenuated influenza vaccine (LAIV) is currently approved in the United States for the prevention of influenza in individuals 2-49 years of age. This article summarizes the available data describing the safety and efficacy of LAIV for the prevention of influenza in both children and adults. LAIV is administered as an intranasal spray and has been shown to provide high levels of efficacy against influenza illness caused by both matched and mismatched strains in children and adults. In studies comparing LAIV and inactivated influenza vaccine in children, LAIV recipients experienced 35-53% fewer cases of culture-confirmed influenza illness caused by antigenically matched strains. Protection through a second influenza season against antigenically matched strains has also been seen in children. In adults, definitive comparative studies of LAIV and inactivated vaccine have not been conducted and no statistically significant differences in efficacy have been demonstrated. The most common adverse reactions with LAIV include runny nose/nasal congestion in all age groups, fever > 100 circle F in children, and sore throat in adults. Formulations of LAIV against pandemic influenza strains, including H5N1, H9N2, and H7N3, are currently being tested in preclinical and phase I clinical studies.