VMD Addresses Leptospira Vaccine Concerns: Benefits Outweigh Rare Risks
The Veterinary Medicines Directorate (VMD) has responded to media and social media discussions concerning adverse events in dogs after receiving Leptospira vaccines (L2 and L4 strains).
The VMD affirms that the benefits of these vaccines surpass their associated risks, noting that the overall incidence of adverse events remains rare.
Vets and pet owners are urged to establish individualized vaccination plans for each dog. These plans should consider local disease risks and other factors detailed in the Summary of Product Characteristics (SPC) or product information.
Adverse Event Incidence Rates
Recent analysis, updated in December 2025, provides the following incidence rates for animal adverse events:
- L2 vaccine products (combined): 0.016%
- L4 vaccine products (combined): 0.040%
This translates to fewer than 2 adverse events reported for L2 vaccines and fewer than 4 for L4 vaccines per 10,000 estimated animals treated. The VMD considers these rates to be rare.
Fatal Adverse Events: A Closer Look
For adverse events resulting in death (including euthanasia), the most recent data indicates:
- L2 vaccine products (combined): 0.0017%
- L4 vaccine products (combined): 0.0033%
This means fewer than 1 animal adverse event involving death was reported for both L2 and L4 vaccines per 10,000 estimated animals treated. The VMD classifies these incidences as very rare.
It's important to note that these incidence figures encompass all received reports. This includes cases involving multiple products, instances of off-label use, or situations where other contributing factors influenced the adverse event.
Vaccine Availability Update
The VMD acknowledges concerns regarding some Marketing Authorisation Holders withdrawing L2-strain Leptospira vaccines. Despite these withdrawals, the VMD assures pet owners that L2-strain vaccines remain available. While the VMD cannot prevent product withdrawals, information on all authorized products in the UK can be found on the Product Information Database.
Defining an Adverse Event
An adverse event is defined as any unfavorable and unintended observation in animals following the use of a Veterinary Medicinal Product (VMP), regardless of whether it is considered product-related.
This definition includes observed side effects or instances where the product did not perform as anticipated.
Ongoing Monitoring
The VMD consistently reviews adverse event report data. This rigorous monitoring ensures that the benefits of all UK-licensed veterinary medicinal products continue to outweigh the potential risks posed by their side-effects.