Direct and Indirect Effectiveness of Influenza Vaccination Delivered to Children at School Preceding an Epidemic Caused by 3 New Influenza Virus Variants

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Abstract
Background. Influenza is an uncontrolled epidemic disease that is vaccine preventable. New recommendations for universal immunization present a challenge to the implementation of vaccine delivery. This field trial examines the effectiveness of school-based clinics for vaccine delivery before an epidemic caused by 3 new influenza virus variants not contained in the vaccine. Methods. Live attenuated influenza vaccine (LAIV) was offered to eligible children in elementary schools of eastern Bell County, Texas. Age-specific rates of medically attended acute respiratory illness for health plan members at the intervention site were compared with those for members at comparison sites during the epidemic, defined by viral surveillance at all sites. Results. Almost 48% of children in elementary schools were vaccinated. Significant herd protection attributed to LAIV was detected for all age groups except 12–17-year-old students, who were not offered free vaccine. Approximately 2500 medical encounters were prevented at the intervention site. Inactivated vaccine provided marginal protection against the epidemic viruses. Conclusions. LAIV delivered to elementary-school children before an epidemic caused by 3 new variant influenza viruses generated significant cross-protection for the recipients and indirect (herd) protection for the community. Trial registration. ClinicalTrials.gov identifier: NCT00138294.

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