Estimating efficacy of trivalent, cold-adapted, influenza virus vaccine (CAIV-T) against influenza A (H1N1) and B using surveillance cultures

M. Elizabeth Halloran, Ira M. Longini, Manjusha J. Gaglani, Pedro A. Piedra, Haitao Chu, Gayla B. Herschler, W. Paul Glezen

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The authors report on a community-based, nonrandomized, open-label study, conducted during the 2000-2001 influenza season in Temple-Belton, Texas, of the protective effectiveness of trivalent, cold-adapted, influenza virus vaccine (CAIV-T) in children aged 18 months-18 years. The dominant circulating strains in 2000-2001 were influenza A/New Caledonia/20/99 (H1N1) and influenza B/Sichuan/379/99. Children had access to CAIV-T during the 1998-1999, 1999-2000, and 2000-2001 influenza seasons. The vaccine included influenza A/Sydney/5/97 (H3N2) and B/Beijing/184/93-like (B/Ann Arbor/1/94) strains in all three seasons. The vaccine included A/Beijing/262/95 (H1N1) in 1998-1999 and 1999-2000, which was replaced by A/New Caledonia/20/99 (H1N1) in 2000-2001. When medically attended acute respiratory illness (MAARI) was used as the outcome, the protective effectiveness for children vaccinated in 2000 was 18% (95% confidence interval (CI): 11, 25). Based on a combination of a validation sample of surveillance cultures and the MAARI outcome, protective efficacy against combined influenza A (H1N1) and B was 79% (95% CI: 51, 91). The efficacy estimate, after accounting for missing influenza culture status, against influenza A (H1N1) alone was 92% (95% CI: 42, 99) and against a new variant of influenza B alone was 66% (95% CI: 9, 87). CAIV-T provides substantial protection against a mixture of influenza A (H1N1) and B. Results demonstrate the powerful potential of using validation sets for outcomes in vaccine field studies.

Original languageEnglish (US)
Pages (from-to)305-311
Number of pages7
JournalAmerican journal of epidemiology
Issue number4
StatePublished - Aug 15 2003

Bibliographical note

Funding Information:
The trial was supported by National Institutes of Health (NIH) grant U01-A141050 and Aviron, now MedImmune Vaccines Inc., Mountain View, California, which also provided the investigational intranasal influenza vaccine. The research of Drs. Halloran, Longini, and Chu was partially supported by NIH grant R01A132042.


  • Culture
  • Data collection
  • Data interpretation, statistical
  • Influenza A virus
  • Influenza B virus
  • Influenza vaccine
  • Vaccines
  • Vaccines, attenuated


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