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January 2004

Direct and Total Effectiveness of the Intranasal, Live-Attenuated, Trivalent Cold-Adapted Influenza Virus Vaccine Against the 2000-2001 Influenza A(H1N1) and B Epidemic in Healthy Children

Author Affiliations

From the Section of Pediatric Infectious Diseases, Department of Pediatrics, Scott & White Memorial Hospital and Clinic, The Texas A&M University System Health Science Center College of Medicine, Temple (Drs Gaglani and Riggs, Mss Herschler and Griffith, and Mr Fewlass); the Departments of Molecular Virology and Microbiology (Drs Piedra and Glezen) and Pediatrics (Dr Kozinetz), Baylor College of Medicine, Houston, Tex; and the Department of Biostatistics, Rollins School of Public Health, Emory University, Atlanta, Ga (Drs Halloran and Longini).

Arch Pediatr Adolesc Med. 2004;158(1):65-73. doi:10.1001/archpedi.158.1.65

Background  The efficacy of the intranasal, live-attenuated, trivalent cold-adapted influenza virus vaccine (CAIV-T) against influenza A(H3N2) and B infections in healthy persons is established, but its effectiveness against natural influenza A(H1N1) infection is unknown.

Objective  To assess the effectiveness of CAIV-T in healthy children during the 2000-2001 influenza A(H1N1) and B epidemic.

Design  Community-based, nonrandomized, open-label trial from August 1998 through April 2001.

Setting  Intervention and comparison communities in central Texas.

Participants  Healthy children, aged 1.5 to 18 years, from the intervention communities received a single dose of CAIV-T at least 1 time or more in 1998, 1999, and/or 2000.

Main Outcome Measures  The incidence of medically attended acute respiratory illnesses during the 2000-2001 influenza epidemic was compared in 3794 health plan CAIV-T recipients with age-eligible, health plan nonrecipients in the intervention communities for direct effectiveness (n = 9325), and with those in the 2 comparison communities for total effectiveness (n = 16 264).

Results  The 2281 CAIV-T recipients in 2000 had significant direct protection against medically attended acute respiratory illness of 18% to 20% during the biphasic influenza A(H1N1) and B epidemic, and 17% to 26% during influenza A(H1N1) predominance. The 931 recipients of CAIV-T in 1999 containing influenza A/Beijing/262/95(H1N1) and B/Beijing/184/93–like viruses had persistent heterovariant protection against the 2000-2001 influenza A/New Caledonia/20/99(H1N1) and B/Sichuan/379/99 variants. The 616 recipients of a single CAIV-T dose in 1999 only, including those younger than 5 years with no prior natural exposure to influenza A(H1N1) viruses, showed persistent protection.

Conclusion  Healthy children who received CAIV-T in 2000 or 1999 were protected against new variants of influenza A(H1N1) and B in the 2000-2001 influenza epidemic.