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Superior Relative Efficacy of Live Attenuated Influenza Vaccine Compared With Inactivated Influenza Vaccine in Young Children With Recurrent Respiratory Tract Infections

Ashkenazi, Shai MD, MSc*; Vertruyen, Andre MD; Arístegui, Javier MD; Esposito, Susanna MD§; McKeith, David Douglas MBChB, MRCGP; Klemola, Timo MD; Biolek, Jiri MD#; Kühr, Joachim MD**; Bujnowski, Tadeusz MD, PhD††; Desgrandchamps, Daniel MD‡‡; Cheng, Sheau-Mei PhD§§; Skinner, Jonathan PhD§§; Gruber, William C. MD§§; Forrest, Bruce D. MB, BS, MD§§for the CAIV-T Study Group

The Pediatric Infectious Disease Journal: October 2006 - Volume 25 - Issue 10 - p 870-879
doi: 10.1097/01.inf.0000237829.66310.85
Original Studies

Background: Young children have a high incidence of influenza and influenza-related complications. This study compared the efficacy and safety of cold-adapted influenza vaccine, trivalent (CAIV-T) with trivalent inactivated influenza vaccine (TIV) in young children with a history of recurrent respiratory tract infections (RTIs).

Methods: Children 6 to 71 months of age were randomized to receive 2 doses of CAIV-T (n = 1101) or TIV (n = 1086), 35 ± 7 days apart before the start of the 2002–2003 influenza season and were followed up for culture-confirmed influenza, effectiveness outcomes, reactogenicity, and adverse events.

Results: Overall, 52.7% (95% confidence interval [CI] = 21.6%–72.2%) fewer cases of influenza caused by virus strains antigenically similar to vaccine were observed in CAIV-T than in TIV recipients. Greater relative efficacy for CAIV-T was observed for the antigenically similar A/H1N1 (100.0%; 95% CI = 42.3%–100.0%) and B (68.0%; 95% CI = 37.3%–84.8%) strains but not for the antigenically similar A/H3N2 strains (−97.1%; 95% CI = −540.2% to 31.5%). Relative to TIV, CAIV-T reduced the number of RTI-related healthcare provider visits by 8.9% (90% CI = 1.5%–15.8%) and missed days of school, kindergarten, or day care by 16.2% (90% CI = 10.4%–21.6%). Rhinitis and rhinorrhea, otitis media, and decreased appetite were the only events that were reported more frequently in CAIV-T subjects. There was no difference between groups in the incidence of wheezing after vaccination.

Conclusions: CAIV-T was well tolerated in these children with RTIs and demonstrated superior relative efficacy compared with TIV in preventing influenza illness.

From the *Schneider Children's Medical Center, Petah-Tikva, Israel; †Sâint Vincentius Hospital, Antwerp, Belgium; ‡Hospital de Basurto, Bilbao, Spain; §Institute of Paediatrics, University of Milan, Fondazione IRCCS “Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena,” Milan, Italy; ¶Townhead Surgery, Irvine, UK; ∥Jorvi Hospital, University of Helsinki, Espoo, Finland; #Hospital Most, Most, Czech Republic; **Clinic for Paediatric and Adolescent Medicine (Stadt Klinikrum Karlsruhe), Karlsruhe, Germany; ††Gabinet Prywatny, Skierniewice, Poland; ‡‡Children's Hospital, Lucerne, Switzerland; and §§Wyeth Vaccines Research, Pearl River, NY.

Accepted for publication July 14, 2006.

This study was funded by Wyeth Vaccines Research and MedImmune.

Address for correspondence: Shai Ashkenazi, MD, MSc, Schneider Children's Medical Center, Department of Pediatrics A, 14 Kaplan St, Petah-Tikva 49202, Israel. E-mail or

© 2006 Lippincott Williams & Wilkins, Inc.