Comparison of the Safety and Efficacy of a Recombinant Feline Leukemia Virus (FeLV) Vaccine Delivered Transdermally and an Inactivated FeLV Vaccine Delivered Subcutaneously
Vet Ther
5[4]:258-262 Winter'04 Review Article 8 Refs
Merial Limited 115 Transtech Road, Athens, GA 30601
The efficacy of a new recombinant feline leukemia
virus (FeLV) vaccine (rFeLV), delivered transdermally (TD) via a needle-free
delivery device, was compared with that of an inactivated FeLV vaccine (FeLV-k)
administered SC with a conventional needle and syringe. Kittens were immunized
with either rFeLV (0.25 mL TD) or FeLV-k (1 mL SC), or they were
sham-vaccinated with physiologic saline (0.25 mL TD). Two vaccinations were
administered 21 days apart. Injection sites were monitored for any acute or
subacute reactions relative to vaccine administration. Four weeks following
the final vaccination, all cats were subject to oronasal FeLV challenge. Blood
was collected for determination of FeLV antigenemia at weekly intervals
beginning 3 weeks after the challenge. All of the vaccinated cats from both
groups resisted FeLV challenge, and 90% of the control cats developed
persistent FeLV antigenemia in response to challenge. No acute or persistent
injection-site reactions were observed. The rFeLV vaccine, delivered TD,
provides protection against persistent FeLV antigenemia following a robust
challenge that is equivalent to that of FeLV-k vaccine.
* Funding for this study was provided by Merial Limited, Duluth, Georgia. *
Study Design:
- recombinant, transdermal FeLV vaccination, 10
kittens - canarypox virus based vaccine with no adjuvants
- canarypox virus expresses the env & gag
FeLV genes
- use of the canarypox virus instead of the FeLV
virus may improve safety
- previously shown effective against oronasal
challenge for up to a year after initial vaccination
- 0.25 ml delivered transdermally via a pressurized
nozzle
- transdermal administration allows for vaccine to
be delivered to a large area of tissue
- nozzle is a single use instrument - inactivated subcutaneous FeLV vaccination, 10
kittens - killed vaccine with adjuvant employing
traditional needle
- sham vaccinated, 10 kttens - 10 kittens were inoculated with saline
transdermally (placebo controls)
Methods:
- kittens tested and found to be FeLV p27 antigen
negative before vaccination
- 2nd vaccine given 21 days after the first in the
caudomedial thigh (opposite thigh used from first vaccination)
- injection sites clipped and monitored after
vaccination
- kittens challenged 4 weeks after 2nd vaccine on 2
consecutive days
- material from NIH given PO and in both nostrils
with kitten under light sedation
- blood samples obtained before challenge, 3 weeks
after challenge and then weekly until 8 of the 10 control kittens were
persistently antigenemic
- persistent antigenemia defined as positive for 3
consecutive or 5 nonconsecutive tests - tester blinded as to group assignment
Results:
- all cats from both Felv vaccinated groups
successfully resisted challenge
- 9 cats in the transdermally-vaccinated group
- 1 of the 10 cats died 17 days postchallenge
- necropsy revealed myocardial degeneration,
suggestive of an underlying pathology unrelated to vaccination or challenge
- all 10 cats in the subcutaneously-vaccinated group
- 1 kitten from each vaccine group was initially
positive at the 21 day postchallenge test and then negative at days 28, 35,
and 42
- 9 of the 10 saline injected control cats developed
persistent antigenemia
- the 10th cat was positive for antigenemia
postchallenge at days 21, 28 and 42 but not 35 days
Clinical Conclusion:
"The recombinant canarypox-vectored FeLV
vaccine, delivered TD via a needle-free device, provides protection against
persistent FeLV antigenemia following a robust challenge, and the protection
is equivalent to that of SC injection of the killed, adjuvanted FeLV
vaccine."
(Purevax® FeLV vaccine Merial)
(VET JET, Bioject Medical Technologies, Tualatin OR)
(Fel-O-Vax® vaccine Fort Dodge)
(Saline placebo control)
(Viracheck, Synbiotics)
