Efficacy of a cold-adapted, intranasal, equine influenza vaccine: Challenge trials

H. G.G. Townsend, S. J. Penner, T. C. Watts, A. Cook, J. Bogdan, D. M. Haines, S. Griffin, T. Chambers, R. E. Holland, P. Whitaker-Dowling, J. S. Youngner, R. W. Sebring

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87 Scopus citations


A randomised, controlled, double-blind, influenza virus, aerosol challenge of horses was undertaken to determine the efficacy of a cold-adapted, temperature sensitive, modified-live virus, intranasal, equine influenza vaccine. Ninety 11-month-old influenza-naïve foals were assigned randomly to 3 groups (20 vaccinates and 10 controls per group) and challenged 5 weeks, 6 and 12 months after a single vaccination. Challenges were performed on Day 0 in a plastic-lined chamber. Between Days 1 and 10, animals were examined daily for evidence of clinical signs of influenza. Nasal swabs for virus isolation were obtained on Day 1 and Days 1 to 8 and blood samples for serology were collected on Days 1, 7 and 14. There was no adverse response to vaccination in any animal. Following challenge at 5 weeks and 6 months, vaccinates had significantly lower clinical scores (P = 0.0001 and 0.005, respectively), experienced smaller increases in rectal temperature (P = 0.0008 and 0.0007, respectively) and shed less virus (P<0.0001 and P = 0.03, respectively) over fewer days (P<0.0001 and P = 0.002, respectively) than did the controls. After the 12 month challenge, rectal temperatures (P = 0.006) as well as the duration (P = 0.03) and concentration of virus shed (P = 0.04) were significantly reduced among vaccinated animals. The results of this study showed that 6 months after a single dose of vaccine the duration and severity of clinical signs were markedly reduced amongst vaccinated animals exposed to a severe live-virus challenge. Appropriate use of this vaccine should lead to a marked reduction in the frequency, severity and duration of outbreaks of equine influenza in North America.

Original languageEnglish
Pages (from-to)637-643
Number of pages7
JournalEquine Veterinary Journal
Issue number7
StatePublished - Nov 2001


  • Challenge trial
  • Cold-adapted
  • Horse
  • Influenza
  • Vaccine

ASJC Scopus subject areas

  • Equine


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