03/09/2026
DID YOUR VET TELL YOU THIS ABOUT THE L4 VACCINE?
Click here to read online: >>> https://www.vincethevet.co.uk/blog/did-your-vet-tell-you-this-about-the-l4-vaccine
Confused about what this vaccine does and doesn't do, and the risks involved in its use?
You're in good company. Understanding all the issues involved when considering whether annual vaccination is beneficial for a particular pet or not, is more complex than it might at first seem.
So let's look at the main issues involved:
1. CLINICAL INFECTION WITH LEPTOSPIROSIS IS RARE, according to available clinical date.
(The strongest population study is the RVC VetCompass analysis of 905,543 UK dogs under primary veterinary care in 2016. It found JUST 7 CONFIRMED CASES, giving an annual incidence of 0.8 cases per 100,000 dogs (0.0008%).
(And on a personal note, I have only seen one confirmed clinical case of leptospirosis in the last 30 years.)
2. THIS BEING THE CASE - WHY VACCINATE AT ALL?
Three reasons are generally given for this:
Firstly: leptospirosis can cause a severe or life-threatening disease in dogs.
Secondly: it is zoonotic (meaning it can affect humans), and so reducing canine infection and urine shedding helps to protect people from contracting the disease.
Thirdly: dogs can encounter infected rodent urine or contaminated water without pet parents being aware they have been exposed to the bacteria, which means severe kidney and / or liver damage can occur before the disease becomes apparent, and antibiotics are given. This in turn can lead to lifelong liver / kidney problems and in some cases death.
3. WHAT DOES THE L4 VACCINE PROTECT AGAINST?
It's important to be aware, that the L4 vaccine offered by vets in the UK DOESNOT PROTECT DOGS AGAINST EVERY TYPE OF LEPTOSPIROSIS.
The vaccine contains four strains representing four important Leptospira serogroups — Canicola, Icterohaemorrhagiae, Australis and Grippotyphosa. As such, it can provide protection against several closely related serovars (serological varieties) within these groups.
However, other leptospiral serogroups are known to occur in the UK AND ARE NOT COVERED BY L4.
This includes Sejroe, which UK research found accounted for around 28% of identifiable high-titre leptospiral serogroup infections in tested dogs—yet Sejroe is not included in the L4 vaccine despite it being one of the 3 most frequently identified serogroups in tested British dogs.
This means that inoculation with L4 does not provide universal protection against leptospirosis.
4. WHAT ABOUT ADVERSE REACTIONS?
It's important when assessing any product given to pets, to consider the frequency and severity of potential side effects.
The current UK Nobivac L4 SPC explicitly lists hypersensitivity, including anaphylaxis, which can sometimes be fatal, as a very rare adverse reaction.
It also lists immune-mediated haemolytic anaemia, immune-mediated thrombocytopenia and immune-mediated polyarthritis, as also being very rare.
More routine transient effects such as injection-site swelling / pain, raised temperature and reduced activity / appetite are cited as being considerably more common.
NOTE:
According to a BSAVA (British Small Animal Veterinary Association) report,THE MAJORITY OF SUSPECTED ADVERSE REACTIONS IN VETERINARY MEDICINE ARE UNREPORTED.
This means official L4 adverse-event rates ALMOST CERTAINLY UNDERESTIMATE THE TRUE FREQUENCY of suspected reactions to some degree (it's not possible to calculate by how much in the absence of verifiable data).
5. INDIVIDUAL FACTORS TO CONSIDER:
The risk of a particular dog being exposed to and developing leptospirosis, in practical terms, comes down to how likely they are to encounter urine from infected rodents, wildlife or livestock, especially in wet environments.
The following factors help to determine whether your pet falls into the higher or lower risk category:
Higher Risk:
- regularly swims or paddles in ponds, lakes, rivers, canals or ditches
- drinks from puddles, streams or other outdoor water sources
- frequent exposure to rats, mice or other wildlife
- hunts, catches or investigates rodents
- lives or walks regularly near farms, livestock, wetlands or waterways
- regular access to muddy, waterlogged or flood-prone ground
- free-roaming or unsupervised outdoor access
- working, gundog or outdoor sporting lifestyle
- frequent countryside, woodland or farm walks
- travel to areas where leptospirosis or additional vaccine-covered serogroups are more prevalent
- local history of confirmed canine leptospirosis or known environmental risk
Lower risk:
- rarely or never enters natural water
- drinks mainly from clean household water
- little obvious rodent or wildlife exposure
- does not hunt or scavenge
- lives mainly in a well-managed urban / suburban environment
- walks mainly on dry, well-drained ground or pavements
- outdoor activity is closely supervised
- predominantly companion / household lifestyle
- limited access to high-wildlife environments
- little or no relevant travel
To summarise:
A higher-risk dog is one regularly exposed to natural water, rodents, wildlife, livestock or wet outdoor environments.
A lower-risk dog has much less contact with these potential sources of infection, although no dog's risk is completely zero.
NOTE:
For vaccination decisions, risk is cumulative.
A dog that occasionally walks in woodland is not necessarily “high risk,” whereas a dog that swims in ponds, drinks from ditches and regularly encounters rats or farm environments, clearly has several important risk factors acting together.
This is why AN INDIVIDUAL BENEFIT-RISK ASSESSMENT for your dog, when considering whether to vaccinate with L4 or not, is important.
And don't forget to take into account the potential for serious and sometimes fatal side effects, which as we have seen, is highly likely to be underestimated by current pharmacological data and adverse event reporting.
THE FINAL DECISION:
In essence, the question to ask, after taking into account local factors (the number of leptospirosis confirmed in the area by your vet over the course of a year, for example) is:
“For my particular dog, is the probability of contracting an L4 preventable form of leptospirosis, higher than the possibility of an adverse reaction to this vaccine?”
Whatever choice is made, it should be the one that brings you the greatest peace of mind.
A WORD ON THE IMMUNE SYSTEM:
A strong, healthy immune system is vital for helping the body cope successfully with exposure to pathogenic microorganisms (and vaccines).
Giving natural supplements which support the immune system in this way, can mean the difference between a pet either succumbing to infection or remaining immune.
Products which are highly beneficial in this respect, in order of potency are:
Vince the Vet:
Immunity
Vitality
Digestion
Detoxification Support
Vet Visit plus Injections(to help the body respond in a balanced way when vaccines are given)
Time Health:
Algal oil
Bio Cultures
If you'd like help with any of the above, please don't hesitate to get in touch via our contact page: >>> https://www.vincethevet.co.uk/contact-us
