Efficacy of a cold-adapted, intranasal, equine influenza vaccine: challenge trials.
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.
Townsend
H G
HG
Department of Large Animal Clinical Sciences, University of Saskatchewan, Saskatoon, Canada.
Penner
S J
SJ
Watts
T C
TC
Cook
A
A
Bogdan
J
J
Haines
D M
DM
Griffin
S
S
Chambers
T
T
Holland
R E
RE
Whitaker-Dowling
P
P
Youngner
J S
JS
Sebring
R W
RW
D000281:Administration, Intranasal; D000818:Animals; D000831:Animals, Newborn; D000914:Antibodies, Viral / Q000097:blood; D001831:Body Temperature; D003080:Cold Temperature; D004311:Double-Blind Method; D006734:Horse Diseases / Q000276:immunology / Q000517:prevention & control*; D006736:Horses; D009980:Influenza A virus / Q000276:immunology* / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology / Q000592:standards*; D009297:Nasal Mucosa / Q000821:virology; D009976:Orthomyxoviridae Infections / Q000276:immunology / Q000517:prevention & control / Q000662:veterinary*; D013997:Time Factors; D016896:Treatment Outcome; D014611:Vaccination / Q000662:veterinary; D014613:Vaccines, Attenuated / Q000276:immunology / Q000592:standards; D017201:Virus Shedding
D000914:Antibodies, Viral; D007252:Influenza Vaccines; D014613:Vaccines, Attenuated