{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T04:05:38Z","timestamp":1784261138975,"version":"3.55.0"},"reference-count":27,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2026,7,16]],"date-time":"2026-07-16T00:00:00Z","timestamp":1784160000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vaccines"],"abstract":"<jats:p>Background\/Objectives: We describe the rationale, design and evaluation of a novel feline combination vaccine (Nobivac\u00ae NXT HCPChFeLV) incorporating RNA particle technology against feline leukemia virus (FeLV) alongside live attenuated components for feline herpesvirus-1 (FHV), feline calicivirus (FCV), feline panleukopenia (FPL) and Chlamydia felis. Efficacy and safety outcomes from laboratory and field studies are presented. Methods: Nobivac NXT HCPChFeLV is a 0.5 mL, non-adjuvanted, lyophilized vaccine containing live attenuated FHV, FCV, FPL, and C. felis strains, and an alphavirus replicon-derived RNA particle expressing FeLV envelope glycoprotein (gp85). The primary vaccination schedule involved subcutaneous vaccination at 8\u20139 weeks of age with a booster 4 weeks later. Onset-of-immunity studies were performed 1 week post primary vaccination. Duration-of-immunity studies evaluated challenge both at 1 year and 3 years after primary vaccination with a booster at 1 year (FHV, FCV, FeLV); FPL duration was assessed at 3 years after primary vaccination; C. felis duration was assessed at 1 year. Clinical signs of disease, survival, leukopenia (FPL) and pathogen excretion were assessed. Safety was assessed in laboratory overdose\/repeat-dose studies and in a field study comparing concurrent (non-mixed) use with rabies vaccination vs a positive control regimen. Results: Vaccination significantly reduced clinical disease following FHV, FCV and C. felis challenge and reduced FHV-associated mortality. Vaccinated cats were protected from FPL clinical disease, mortality, leukopenia, and FPL excretion. Persistent FeLV antigenemia was significantly prevented after primary vaccination and in 1-year-duration-of-immunity studies and was reduced 3 years after revaccination. The excretion of FHV, FCV and C. felis was significantly reduced in vaccinates vs controls. No serious adverse events were observed in laboratory studies; field vaccination was well tolerated with no injection-site reactions reported. Conclusions: Nobivac NXT HCPChFeLV provides robust, long-lasting protection against multiple feline pathogens, reduced pathogen shedding and demonstrated a favorable safety profile, supporting its use in feline preventive healthcare.<\/jats:p>","DOI":"10.3390\/vaccines14070625","type":"journal-article","created":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T03:12:38Z","timestamp":1784257958000},"page":"625","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Development of a New Feline Combination Vaccine Including a Novel RNA Particle Vaccine Against Feline Leukemia Virus"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-0830-3297","authenticated-orcid":false,"given":"Willem","family":"Huisman","sequence":"first","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aart","family":"Mommen","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephanie","family":"Basten","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kim","family":"Driessen","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter","family":"Pepels","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7104-4719","authenticated-orcid":false,"given":"Qi","family":"Cao","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hans","family":"Holtslag","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Melissa Ann","family":"Bourgeois","sequence":"additional","affiliation":[{"name":"Merck Animal Health, Rahway, NJ 07065, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jacqueline","family":"Pearce","sequence":"additional","affiliation":[{"name":"MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,16]]},"reference":[{"key":"ref_1","unstructured":"Advisory Board on Cat Diseases (2025, June 17). 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