Vaccination is fundamental to feline preventive healthcare, protecting against potentially fatal diseases including feline herpesvirus, calicivirus, panleukopaenia, and in some cats, feline leukaemia virus. Adverse reactions range from mild and transient to severe and rare. Understanding the spectrum of reactions enables informed welfare decisions about vaccination.
Common Mild Reactions
Most adverse reactions to vaccines are mild and transient:
- Local swelling and tenderness at injection site — peaks 24–48 hours post-vaccination, resolves within 1–2 weeks
- Lethargy and reduced appetite for 1–3 days post-vaccination — very common, particularly after killed (adjuvanted) vaccines
- Mild fever — self-limiting
- Sneezing and mild respiratory signs after intranasal modified-live vaccines (FHV-1, FCV)
These reactions require no treatment — cold compress on injection site and monitoring are sufficient. They do not contraindicate future vaccination.
Hypersensitivity Reactions
Anaphylaxis and acute allergic reactions occur rarely:
- Signs: vomiting, diarrhoea, facial swelling, urticaria, respiratory distress, collapse — within minutes to 30 minutes of vaccination
- Management: adrenaline, IV fluids, antihistamines, corticosteroids
- Cats with previous anaphylaxis to a vaccine should be pre-treated with antihistamines before subsequent vaccination — or the antigen reconsidered
Feline Injection Site Sarcoma (FISS)
FISS is a rare but serious complication — aggressive soft tissue sarcoma developing at injection sites, occurring in approximately 1–10 cats per 10,000–100,000 vaccinations. Historically linked to aluminium-adjuvanted vaccines. Key welfare guidance:
- Any lump at an injection site persisting >1 month after vaccination, >2cm in size, or growing in size should be biopsied immediately — early excision with wide margins is the only effective treatment
- Injection sites have been standardised (right foreleg for rabies, left foreleg for FeLV, right hindleg for FVRCP) to enable complete surgical limb amputation if FISS develops
- Non-adjuvanted (modified-live or recombinant) vaccines are preferred where available to reduce FISS risk
Vaccination Decision-Making
Core vaccines (FHV-1, FCV, FPV) are recommended for all cats — the disease prevention benefit far outweighs FISS risk. Non-core vaccines (FeLV, FIV, rabies) are given based on individual risk assessment. Vaccination intervals should follow the WSAVA guidelines — triennial revaccination for core vaccines in adult cats with documented primary series reduces injection frequency while maintaining protection.