Herd protection against influenza.

Mortality and hospitalization rates due to influenza have risen despite increasing vaccine coverage for the most vulnerable population; however, those most vulnerable to complications and death are the least likely to respond to the vaccine. New strategies for influenza control are needed and indirect effectiveness (herd protection) has been demonstrated for several currently used vaccines - rubella, H. influenzae type b, pneumococcus varicella and hepatitis A. The Japanese schoolchildren program provided proof of concept of indirect effectiveness of influenza vaccine. The Central Texas field trial has demonstrated significant herd protection of adults utilizing the live, attenuated influenza vaccine (LAIV) to children. Immunization of <20% of children at the intervention site resulted in an 8-18% reduction of medically attended acute respiratory illness in adults compared to rates in the comparison sites. LAIV given by nasal spray is efficacious against matched and poorly matched prevalent strains, easy to administer and readily accepted by children for annual immunization. School-based clinics could provide a platform for rapid deployment of vaccine accessible to all segments of the population. This strategy could be critical for control of pandemic influenza.