Evaluation of safety and immunogenicity of feline vaccines with reduced volume.

A non adjuvanted vaccine against feline herpesvirus, feline calicivirus, feline panleucopenia and feline leukemia has been formulated in reduced volume (0.5 ml) with the same antigen content as the conventional 1 ml presentation. This paper reports studies evaluating the safety and the immunogenicity of this reduced volume vaccine in comparison with the conventional volume vaccine. The safety of both vaccines was evaluated in a small sized laboratory trial. It was further tested in a randomized controlled field trial on a total of 398 cats. Immediate and delayed local and systemic adverse events were monitored after vaccination. The immunogenicity of each vaccine was also checked by serological antibody responses against the vaccines antigens during the laboratory trial. These studies showed that the 0.5 ml vaccine was well tolerated in cats, inducing less local events, while keeping the same immunogenicity as the corresponding 1 ml vaccine. Reducing the volume of the vaccine is a way to improve the convenience of administration and to help following vaccination guidelines with the aim of reducing the incidence of adverse events following vaccination.

Efficacy of a nonadjuvanted recombinant FeLV vaccine and two inactivated FeLV vaccines when subject to consistent virulent FeLV challenge conditions.

The purpose of this study was to compare the efficacy of three FeLV vaccines, under identical conditions in a laboratory challenge model that closely mimics natural infection. Four groups of cats (n = 20 per group) were administered two doses of vaccine, 21 days apart, starting at 9-10 weeks of age (Purevax® FeLV, Versifel® FeLV, Nobivac® feline 2-FeLV, and a placebo). Cats were challenged 3 weeks later with a virulent, heterologous FeLV isolate. FeLV antigenemia was determined at weekly intervals from 3 to 15 weeks postchallenge. Circulating proviral DNA was determined on terminal PBMC samples. Following challenge, persistent antigenemia developed in 15 (75%) placebo-vaccinated cats, 3 (15%) cats in the Versifel FeLV vaccinated group, and 1 cat (5%) each in the Purevax FeLV and the Nobivac FeLV vaccinated groups. The prevented fractions for three vaccine groups were 93%, 93%, and 80% respectively. The adjusted p-values for all vaccine group comparisons fail to approach statistical significance. There was excellent agreement between proviral FeLV DNA in circulating PBMCs and persistent antigenemia. It is shown that when cats are managed under the same conditions during a virulent challenge, via the normal route of infection, the tested vaccines all show a comparable degree of protection.

Three-year duration of immunity for feline herpesvirus and calicivirus evaluated in a controlled vaccination-challenge laboratory trial.

Feline vaccination guidelines recommend less frequent boosters for the core vaccines (rhinotracheitis, calicivirosis and infectious panleucopenia). Most guidelines recommend boosters at 3-yearly intervals after a basic vaccination including primary vaccination and revaccination one year later. The objective of this study was to assess the duration of immunity induced by PUREVAX(®) RCPCh FeLV, a non-adjuvanted vaccine against feline rhinotracheitis, calicivirosis, infectious panleucopenia, chlamydiosis and leukemia. After primary vaccination followed by revaccination one year later with a vaccine formulated at minimum dose, the cats were kept in a confined environment and challenged 3 years later with a virulent heterologous strain of feline calicivirus (FCV) and subsequently a virulent strain of feline herpesvirus (FHV). Clinical signs and viral excretion were recorded for two weeks after each viral inoculation. Contemporary unvaccinated cats and new animals added at the time of challenge were used as controls. The vaccination regimen induced a stable and long-lasting humoral response. Vaccination resulted in a significant reduction in the severity of the disease after FHV challenge and in the frequency of cats showing a severe calicivirosis (defined as a combination of systemic clinical symptoms and oronasal ulcers). As opposed to the significant reduction of excretion observed a few weeks after primo-vaccination or even one year after vaccination for FCV, viral shedding was not reduced 3 years after revaccination. This study showed that primary vaccination and revaccination one year later with PUREVAX(®) RCPCh FeLV was able to induce 3-year duration of immunity against FCV and FHV. The results and conclusion of this study are consistent with current vaccination guidelines and will allow the veterinarian to adapt the vaccination regimen to the way of life of the cat.