My dog’s had the L2 but not the L4 – should I upgrade?

This is a really interesting question, and one that a lot of animal owners have been asking. There are also different views by vets – on a quick “straw poll” in our office, we have had three different answers so far! Ultimately, it boils down to questions of effectiveness, safety, cost and convenience – but in this blog we are going to try and use evidence to determine what the best solution is in the real world.

What is the lepto vaccine for?

As the name suggests, the vaccine provides limited, but fairly effective, protection against Leptospira infection. This is caused by a group of bacteria called leptospires that are spread in the urine of infected animals, primarily rats. The bacteria can infect many animals, including dogs, cattle and humans, and may lead to liver damage, kidney failure, and are potentially fatal, with UK vets reporting a 60% mortality rate in infected dogs. That said, clinical infection is relatively uncommon, possibly as a result of relatively widespread vaccination – while the vaccine does not prevent infectionwith leptospires, it is pretty good at preventing that infection from causing clinical disease, and excellent at preventing the patient from becoming a carrier, infecting other dogs, animals or people.

What’s the difference between the two vaccines?

The main difference is that the L2 contains only 2 strains of leptospire – Icterohaemorrhagiaeand Canicola. Historically these were the most common types seen – however, in recent years others have been increasingly being seen and in the L4, the manufacturers made two changes – firstly, they increased the amount of antigenic compound (i.e. how many dead bacteria were present), and secondly they added two additional strains, Australis(the group containing the specific strain Bratislava) and Grippotyphosa (reported to be the most common strain in much of Europe). Contrary to popular belief, there has been no change in the adjuvant component of the vaccine between the two versions.

Why are some puppies being started on L2 anyway?

Originally, the manufacturers of the L4 series of vaccines (Intervet, a subsidiary of Merck’s MSD Animal Health division) had intended to phase out the L2 vaccine, and entirely replace it with L4.

However, there has been a widely publicised campaign reporting large numbers of deaths and other harmful effects from the vaccine, and a lot of breeders refuse to use it; as a result, many vets offer either the L4 or the L2.

Is the L4 vaccine really dangerous?

It depends how you define your terms! Ultimately, any medication is potentially dangerous – a drug that never has any side effects at all is, sadly, either a myth or a product that doesn’t doanything at all. As soon as you start altering or tweaking the physiology of an organism as complex as a mammal, there is the potential for unexpected and undesirable results. In actual fact, vaccines as a whole are much safer than most medicines, because they are actually far more natural than any pharmaceutical or herbal medicine.

We need to remember what a vaccine is – essentially, it’s not intended to alter the animal’s physiology or biochemistry. Instead, we can think of it as being like a flight simulator – it allows the immune system to “practice” how to fight an infection, with a lower (or in the case of a killed vaccine like Lepto, zero) risk of real infection. However, there is always the chance of the immune system “overreacting”. As a result, both the manufacturers and the regulators are required to keep data as to how many suspected adverse reactions occur.

For L2, the risk is 0.015% of a suspected adverse reaction – so of 10,000 dogs given the vaccine, we would expect 2 to become ill enough to require treatment, and therefore get a report of a significant side effect. For L4, the risk ishigher, at 0.069% (so 7 in 10,000). This is a similar risk to you developing anaphylactic shock, an asthma attack, or a bleed on the brain after taking an aspirin tablet– it can happen, but it probably won’t.

What about all the dogs who are supposed to have died?

Hundreds of thousands of doses of L4 are given every year – sadly, sooner or later statistically some dogs will develop more serious problems, some of which may be fatal. The trouble is that a “suspected adverse reaction” may or may not actually be due to the vaccine – it could be that the patient developed some disease at a similar time, that it was due to some other component in the combination vaccine given, or (most commonly of all) that the dog was examined by a vet who noticed the problem at the time of vaccination.

That said, there is a very real possibility that any vaccine can trigger an autoimmune disease. Is this really a vaccine related event? The consensus of opinion is that these dogs would sooner or later experience autoimmune disease, as they were genetically predisposed to do so – either triggered by a vaccine, or by a natural infection, it wouldn’t really matter.

Overall, though, dogs having L4 are roughly 3 ½ times more likely to become unwell than dogs having L2.

So, is it worth it?

Now here’s the rub! Unfortunately, there is no central database for how many Leptospirosis cases there are in the UK that are due to each serotype of the bacteria. We are pretty sure that Grippotyphosais not natively found in the UK (although this would be relevant to any dogs visiting Europe). However, in 1991 a major study was conducted in Edinburgh and Glasgow and found that just over 6% of dogs had been exposed to Bratislava (part of the Australis group) – and of those dogs testing positive for exposure to any Lepto strain, 5% were actively excreting Bratislava bacteria.

Assuming a 5% risk of infection at any one time, this means that 1 in 20 (500 in 10,000) of the L2 but not L4 vaccinated dogs poses a risk to others of spreading Leptospira bacteria; assuming that 98% of cases are subclinical, then 0.1% (10 in 10,000) will get ill – a rather higher number than the risk of suspected adverse reactions.

So overall, based on the evidence we have now, yes, you are better off vaccinating against L4 than just limiting it to L2.

How do we move forward?

There are three options –

  • Get them upgraded now. This will, however, cost more and be inconvenient, for a relatively small benefit to your dog.
  • Don’t upgrade, just keep them on L2. This is cheapest and most convenient, but does mean that there’s a substantial risk that they will be shedding the bacteria, and there is still a markedly increased risk of harm.
  • Upgrade when your dog is next due their vaccination. This is probably the best “compromise” position.

Overall, it’s really important that you and your vet agree a vaccination plan for your dog as an individual. Also, don’t trust online scaremongering – there are lots of very misleading websites out there (mainly anti-vaccination, but some over enthusiastically pro-vaccine as well) whose output is based entirely on emotion and illogic, rather than evidence and clinical reality.


6 thoughts on “My dog’s had the L2 but not the L4 – should I upgrade?

  1. Thank you for your information I am thinking of buying a puppy in the UK and I had notice that some of the breeders said they used the L 2 and not the L4 and I wonder what was the diffeance.

  2. Our Golden retriever died 5 weeks after having the l4 vaccine and 1 week after the top up. We had moved with our usual vet to his own practice and was told by him when it came to Tilly’s annual booster, that they administered this vaccine!! We had nothing but good faith in him.!!
    Tilly, whilst 11 years old was fit and healthy and was told so by the vet the week the vaccination was administered.
    A week after the top up, Tilly suddenly collapsed and there followed numerous emergency tests including every cancer imaginable and some tested twice. Her blood count had plummeted and her platelets very very low. The conclusion was hard to diagnose with an auto immune disease the most likely. All symptoms now pointing to the vaccine, which even the Vet mentioned but when questioned, tried to talk about anything and everything but the vaccine! We then did our research as was shocked to see the results of thousands of dogs in the UK alone had died from the vaccine. Let alone around the world. Basically on reading because millions of dogs were saved by vaccines the thousands that had died where basically collateral damage!! Heartbreaking for any owner to read this. Tilly was, as have all our dogs, been our babies and loved and cared for doing everything in our powers to keep her and them safe, for this to happen. read on…
    The week Tilly dies, on the Monday we had some good news that her blood count had started to rise with the Vet telling me he could be cautiously optimistic !! So much so i felt i did not have to have so many carers in to help sit her! So WRONG…
    On the Thursday, 3 days before Christmas after popping out i had an uneasy feeling Tilly was not right and on returning home to find her collapsed on her bed looking back at me. The look told me everything and i placed her in my arms and she gave a little whimper and i knew this was the end. Calling the vet who got stuck in traffic along with my husband also stuck, Tilly was in agony for two hours struggling to breath. Finally the vet came and was not able to stop her agony by helping her to go to sleep!! Her veins had all flat lined, another example of the auto immune disease. She finally died in awful agony. That experience broke us and all where crying for our beautiful girl.. I will never forget or forgive the vet. For us, no matter what you vets may say about keeping animals safe, exactly how much are you all influenced by others to take this vaccine!!!
    My Tilly was not collateral damage, she was a much loved, spoilt gorgeous dog rescued from cruelty at the age of 4 with half her body weight and coat tin an awful state and beaten to be killed mercilessly a few years later for trying to keep her healthy.
    So you ask, should you upgrade from L2 to L4? No No No never.
    WE are now owners of a cockapoo and are terrified of vaccines but have allowed the puppy ones and still, after talking to our original vets concerned about his annual boosters but are caught between vets and insurance companies who insist on vacination!!
    There is a titer test that can be taken to determine to see if the dog is still virus free and are considering this before going ahead with boosters. This experience has scarred us for life and will never get over it, Vets need to be more aware of how vaccinations can have adverse reactions on dogs….
    This is not on line scaremongering as you say. This is FACT, an awful awful FACT. Do not undermine genuine dog lovers who keep their dogs healthy only to be let down by vetinary practices!!

    1. I’m so sorry you’ve had this experience – losing a pet in such a horrible way is always awful. Although adverse reactions are really rare in practice, they’re awful when they do occur, especially when the reason for it isn’t entirely clear. I’m sure either your vet will have reported this to the VMD as a suspected adverse reaction, but if you’re not sure, you can submit a report yourself here:

  3. My neighbours healthy 7 year old Westie died 3 days after having a annual booster. The little dog collapsed and died in the garden. Another local dog (a two year old Springer Spaniel) had a booster and died the next day! DO NOT HAVE ANNUAL BOOSTERS DONE! Your dogs don’t need it! It’s a money getting game by Vet’s!

    1. I’m really sorry to hear about your dog; please accept my condolences.
      However, dogs do need annual boosters if they want protection from Leptospirosis, parainfluenza, and kennel cough, among others. Very, very few vets give parvo, distemper or hepatitis annually – it’s well known that these components last 3+ years, and as recommended by the WSAVA and the manufacturers, I don’t know any vets who do vaccinate against these components every year. There’s evidence to suggest many, possible most, dogs maintain immunity to parvo, in particular, for many years, but some do not; in this situation, revaccination every 3 years or titre tests to see how long the immunity lasts are more appropriate. There are no such tests for the other diseases (kennel cough, parainfluenza, leptospirosis etc), and the evidence suggests that these vaccines do not last more than 12-15 months. There’s some great information about the safety and effectiveness of modern vaccines compiled by the WSAVA’s Vaccine Group here:

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