FIV vaccine: still no licensed product, but new approaches

Feline immunodeficiency virus (FIV) — sometimes called feline AIDS — remains one of the most significant unmet needs in cat medicine. Unlike FHV-1, FCV, and FPV, which are addressed by the core vaccination schedule, FIV has no currently licensed vaccine in Europe or the UK.

The last commercially available FIV vaccine (Fel-O-Vax FIV, licensed in the US and Australia) was discontinued in 2017 following questions about its interference with serological testing and variable field efficacy. Since then, several research groups have been developing subunit and viral vector-based approaches that avoid these drawbacks.

A 2026 preprint from researchers at the University of Edinburgh describes a mRNA-based FIV vaccine candidate that elicited neutralising antibody responses in a small cohort of specific-pathogen-free cats. The work has not yet entered clinical trials, but represents the most advanced mRNA approach published for feline viral disease to date.

Current FIV prevention advice

  • Neuter male cats — FIV is primarily spread through bite wounds during territorial fights
  • Keep high-risk cats (outdoor, unneutered males in areas with known FIV prevalence) indoors or in cat-safe enclosures
  • Test new cats before introducing them to a resident FIV-negative cat
  • FIV-positive cats can live normal lives indoors, away from uninfected cats

Allergen vaccines: reducing Fel d 1 in cats

One of the most commercially significant areas of feline vaccine research targets not cat disease but human cat allergies. Roughly 10–20% of the global population is allergic to cats, with Fel d 1 — a small protein produced primarily in cat saliva and sebaceous glands — as the dominant allergen.

Swiss biotech HypoPet has continued Phase II development of HypoCat, a vaccine that immunises cats against their own Fel d 1, causing the immune system to produce antibodies that neutralise the protein. Early results published in the Journal of Allergy and Clinical Immunology showed a significant and durable reduction in active Fel d 1 levels in vaccinated cats. A companion Phase III trial is expected to report results in 2027.

A separate approach — immunotherapy for the human rather than the cat — has also advanced. The AstraZeneca–Circassia biologic programme showed earlier mixed results, but successor compounds targeting Fel d 1 directly have shown more promise in early trials.

FCV strain coverage: addressing virulent systemic strains

Feline calicivirus (FCV) mutates rapidly and exists as a large population of diverse strains. The virulent systemic FCV (VS-FCV) that emerged in the 2000s causes severe disease including facial oedema, limb oedema, and mortality even in previously vaccinated cats.

The current standard is to include two FCV strains in vaccines (F9 and 255 are the most common). Research groups in the Netherlands and Japan have been exploring how many additional strains would be needed in a polyvalent vaccine to achieve broad protection — early modelling suggests four to six strains would cover the majority of circulating genotypes, though manufacturing and regulatory complexity increases substantially with each additional strain.

Practical implications for cat owners

For most cat owners, the practical takeaway from 2026 research is this: existing core vaccines remain the evidence-based standard. None of the emerging products are yet commercially available. Keep your cat's vaccinations current using the schedule your vet recommends — see our cat vaccinations guide for what is due and when.