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Attenuated vs. Inactivated Flu Vaccine in Children: Benefits and Adverse Effects

An investigational attenuated flu vaccine has superior efficacy to standard inactivated vaccine, but it comes with a significant risk for medically important wheezing.

In the U.S., vaccination with intramuscularly administered trivalent inactivated influenza vaccine (TIV) is recommended for all children aged 6 to 59 months. However, live attenuated influenza vaccines may provide better protection than TIV and are administered intranasally. One such vaccine is already recommended in the U.S. for people aged 5 to 49 years.

In a manufacturer-supported, randomized, double-blind trial conducted during the 2004–2005 influenza season, researchers compared the efficacy and safety of TIV with those of an investigational cold-adapted attenuated trivalent influenza vaccine (CAIV-T) in 6- to 59-month-old children. Participants were enrolled at 249 outpatient sites in the U.S., Europe, the Middle East, and Asia. Safety data were available for 8352 children; 7852 were included in the per-protocol analysis.

CAIV-T recipients had 55% fewer cases of culture-confirmed influenza than did TIV recipients (153/3916 vs. 338/3936; P<0.001). The reduction in cases was greatest for influenza A virus (89% for H1N1, 79% for H3N2; both P<0.001) and least for influenza B virus (16%; P=0.19). Reduction in cases was seen with both antigenically well-matched (44%) and mismatched (58%) influenza viruses.

Among 6- to 12-month-old children, medically significant wheezing 6 weeks postvaccination was more common with CAIV-T than with TIV (4% vs. 2%). By 180 days postvaccination, wheezing had occurred in 14% of CAIV-T and 10% of TIV recipients, and hospitalization for any cause had occurred in 6% of CAIV-T and 3% of TIV recipients. CAIV-T recipients aged 12 to 48 months with past histories of wheezing showed a trend toward higher any-cause hospitalization rates.

Comment: Clearly, CAIV-T is superior to TIV in preventing influenza A disease in infants and young children, and it has a more acceptable route of administration. This superiority, however, seems to come at a substantial price — an increased incidence of wheezing, particularly in children <12 months old. I agree with the editorialists, who urge further discussion and careful review of the safety data for CAIV-T before any decisions are made regarding the use of this vaccine in infants and young children.

— Neil R. Blacklow, MD

Published in Journal Watch Infectious Diseases February 14, 2007

Citation(s):

Belshe RB et al. Live attenuated versus inactivated influenza vaccine in infants and young children. N Engl J Med 2007 Feb 15; 356:685-96.

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• Medline abstract (Free)

Cox NJ and Bridges CB. Inactivated and live attenuated influenza vaccines in young children — How do they compare? N Engl J Med 2007 Feb 15; 356:729-31.

• Original article (Subscription may be required)
• Medline abstract (Free)