Duration of protection provided by live attenuated influenza vaccine in children

Background: Reliable availability of influenza vaccine before October could enable the vaccination of many children who might not otherwise be vaccinated. Methods: Available data for children were analyzed to describe protection provided by live attenuated influenza vaccine (LAIV) for greater than 5 months postvaccination. Results: Four studies conducted in children aged 6 months to 18 years were identified. Culture-confirmed efficacy against A/H1N1 and A/H3N2 strains at 9-12 months postvaccination was 77% [95% confidence interval (Cl): 53-89%] to 100% (95% Cl: 68-100%) and through a second influenza season without revaccination was 56% (95% Cl: 31-73%) and 57% (95% Cl: 6-82%), respectively. Against B strains, I study demonstrated 86% (95% Cl: 59-95%) efficacy at 5-7 months. Another study demonstrated 27% (95% Cl: -62% to 67%) efficacy at 9-12 months compared with 74% (95% Cl: 39-89%) at 1 to < 5 months during a period of antigenic drift for circulating B strains. A third study estimated 50% (95% CI: -49% to 83%) efficacy against influenza B strains through a second season without revaccination. Conclusions: In children, live attenuated influenza vaccine provided sustained protection against influenza illness caused by antigenically similar strains. Efficacy at 1 to < 5 months postvaccination was comparable to that at 9-12 months for A/H1N1 and A/H3N2 strains and at 5-7 months for B strains. Meaningful efficacy was seen through a second season without revaccination, although at a lower level than during the first 12 months postvaccination.