Bold opening: Leptospira vaccines for dogs are safe overall, despite online alarm—and the real story is about rare risks vs. clear benefits. But here’s where it gets controversial... the details behind the numbers you’ll want to understand before deciding what’s best for your pet.
The UK’s Veterinary Medicines Directorate (VMD) has issued a routine update on adverse event data for Leptospira vaccines that come in two strains (L2) or four strains (L4). They emphasise that vaccination plans should be tailored to each dog, taking into account local disease risk and other factors listed in the product information.
What the data say
- For all UK-approved vaccines that contain two Leptospira strains (L2), the latest December 2025 analysis shows an adverse-event incidence of 0.016% across all L2 products combined.
- For vaccines with four Leptospira strains (L4), the incidence is 0.040% across all L4 products combined.
- In plain terms, fewer than 2 adverse events per 10,000 treated dogs for L2, and fewer than 4 per 10,000 for L4—indicating these events are very rare.
Deaths linked to adverse events
- The most recent data show death-related adverse events (including cases leading to euthanasia) at 0.0017% for all L2 products, and 0.0033% for all L4 products.
- That equates to fewer than 1 death per 10,000 treated dogs for each vaccine category, under the figures provided.
Notes on the figures
- The reported incidences cover all reports received, including cases where more than one product was used, off-label use (not following manufacturer guidance), or where other factors fully explained the adverse event.
- For context, the 2023 GOV.UK update on Leptospira vaccination in dogs remains a reference point for earlier incidence data.
Availability concerns
- Some vaccine manufacturers have withdrawn two-strain Leptospira vaccines from the market, which has prompted questions about availability.
- The VMD reassures that vaccines containing two strains are still available. They note they cannot compel manufacturers to keep products on the market, but you can verify options via the UK Product Information Database.
What is an adverse event?
- An adverse event is any observation in an animal after using a veterinary medicinal product (VMP) that is unfavourable or unintended, whether or not it’s directly caused by the product. This includes side effects or failures to produce the expected effect.
Post-approval monitoring
- The VMD continuously reviews adverse-event reports to ensure the benefits of every licensed veterinary product outweigh potential side effects.
Bottom line and practical takeaway
- Leptospira vaccines (L2 and L4) have very rare associated adverse events, and the overall benefit to canine health remains favorable when vaccines are used as part of a tailored, risk-based vaccination plan.
- If you’re unsure which vaccine is appropriate for your dog, consult your veterinarian to assess local disease risk, your dog’s health history, and any other risk factors listed in the product information.
Discussion prompt
Is your view that vaccination should be customized to each dog’s risk, or do you prefer a standard, universal schedule? Share your thoughts and experiences in the comments to spark a thoughtful discussion.
