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 (CI): 53–89%] to 100% (95% CI: 68–100%) and through a second influenza season without revaccination was 56% (95% CI: 31–73%) and 57% (95% CI: 6–82%), respectively. Against B strains, 1 study demonstrated 86% (95% CI: 59–95%) efficacy at 5–7 months. Another study demonstrated 27% (95% CI: −62% to 67%) efficacy at 9–12 months compared with 74% (95% CI: 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.