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Duration of Protection Provided by Live Attenuated Influenza Vaccine in Children

Ambrose, Christopher S. MD; Yi, Tingting PhD; Walker, Robert E. MD; Connor, Edward M. MD

The Pediatric Infectious Disease Journal: August 2008 - Volume 27 - Issue 8 - p 744-748
doi: 10.1097/INF.0b013e318174e0f8
Review Articles

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.

From MedImmune, Gaithersburg, MD.

Additional material related to this article and only published online can be accessed on the Web by clicking on the “ArticlePlus” link either in the Table of Contents or at the top of the Abstract or HTML version of the article.

Accepted for publication March 17, 2008.

Studies were funded by Wyeth Vaccines Research and MedImmune.

Address for correspondence: Christopher S. Ambrose, MD, MedImmune, One MedImmune Way, Gaithersburg, MD 20878. E-mail:

© 2008 Lippincott Williams & Wilkins, Inc.