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.


71 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.

    1. Thank you for your article which is very helpful. I have a question: is it not possible for manufacturers to develop individual vaccines for each illness, particularly for Leptospirosis, given spaced out, or would that be worse for the dog with more different shots and impractical for some owners and more expensive. If a dog was very unfortunate in having a reaction and any vaccines had been given separately, would this not make it easier to trace the component where the reaction had come from? Just a thought

      1. It’s theoretically possible. However – most of the problems with killed vaccines come from the adjuvant, rather than the antigen, and you need almost the same dose of adjuvant for 4 antigens as for 1. So I doubt it would make much difference in practice!

  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:

    2. So sorry you and especially your dog went through this. All I can say is that the vet gives best advice based on the information they have. Even L2 vaccines carry a degree of risk and other dog owners will have had a similar experience to yours with that virus. I personally take medication which has side effects and risks. We have to weigh these up all the time.
      Where I live there are increasingly wild boar encroaching on the areas I walk my dog so I will be taking the L4 vaccine as wild boar have been shown to carry the bratislava strain of the virus. It won’t be the same for other dog owners whose dogs are not exposed to that virus on a regular basis.
      I pray my dog does not have an adverse reaction.
      I hope your current pets are fit and healthy and stay that way.

    3. I recently had a bad experience with this vaccine I had a beautiful litter of border collies 3 boys 4 girls, all healthy good size and progressing well. I booked them into the vets where my puppies mum is registered for their 1st injections and microchips, I never got a choice of which strain I wanted them to have anyway the vaccines was given to all my puppies their was some little cries from some of them. Anyway the next evening my partner noticed that one of the little boys was making strange noises whilst trying to breath so he picked him up and laid on the sofa with him I noticed that he was burning red hot so tried to cool him down by laying him on our laminate floor he was there for about 20 minutes before he had a massive seizure that’s when we knew there was something seriously wrong so I got him in to the emergency vets, 4 more seizures on the way there, once there they checked him over he became blind and brain damaged due to the seizure and lack of oxygen it felt like they was accusing us of hurting him as they kept referring to it looking like he had sustained a head injury (we had been with him all the time not left their sides) so we knew it wasnt he was healthy before that vaccine, strong healthy hearts and good weight according to our vets. We was advised to have him put to sleep as their was nothing they could do for him with how young he was. Devastated was an understatement I had watched this little puppy grow and he had just started to show his little personality. He never got to feel grass under his feet or have his 1st walk. So I’m totally with you on this matter I will never allow that vaccine again they are not collateral damage they are living breathing creatures and loved family members and I will advise anyone that I know that’s gets a new fur baby to no go for that vaccine.

      1. I’m so sorry to hear about your puppy.
        It’s a really hard call to make, isn’t it – do we vaccinate knowing there’s a very small but real risk of side effects; or do we not and take the risk of a life-threatening (and contagious) infectious disease?
        Personally, my dogs are vaccinated with the L4 vaccine because I’ve seen the effects of Lepto in unprotected dogs, but that doesn’t help when something does go wrong that seems to be linked to what we’ve done. Statistically the vaccine is very safe – but like any medicine, it’s not perfect. Don’t blame your yourself or your vet – this is a horrible thing but it’s not anyone’s fault. Rather it’s a tragic concatenation of circumstances that probably couldn’t have been predicted.
        I would strongly advise that you get a formal autopsy performed to help determine exactly what went wrong, and forward the results to the Veterinary Medicines Directorate (the UK’s animal medicine and drugs regulator) so they are aware of what’s happened and why, and can work with the manufacturer to help improve the vaccine’s safety.

    4. Which did you give yr new pup L2 or L4. As getting a pup soon and dont know which ti give after my dog dying aged 11 6weeks after having booster L4 with auto immune disease I’m convinced it was the booster that killed her. As a pup she had her first injection and developed puppy strangles which is an auto immune disease. But worried if the L2 is enough cover.

      1. It is certainly possible that the vaccine triggered a latent autoimmune disease, but it is statistically unlikely. On the continent there’s an L6 which is regularly used, as there are more pathogenic strains in central and Eastern Europe than over here, but we definitely have 3 of the 4 in L4 present and causing infections in the UK.

  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:

      1. I think it’s disgusting that vets do not promote titre testing. I lost 2 dogs at 5 yrs old and I am sure over vaccinating, continual worming and flea treatments caused their deaths. I refuse to put any chemicals in my dogs. My dogs haven’t needed a booster for 4 yrs now. They also haven’t had worms for 5 years, I get their poo checked but my vet always asked if their worming is up to date… NO, BECAUSE THEY HAVENT GOT WORMS.

        1. Faecal counts aren’t terribly good at detecting worms, unfortunately. And virtually all puppies are born with some worms – because of their biology, we have to assume that all dogs have at least some pretty much all of the time.
          Modern vaccines and flea treatments are among the safest medications that have ever existed; that said, like any effective intervention, they do have some side effects. I assume you got post mortem examinations on your dogs to determine the causes of death? If there’s any possibility that it’s due to a medicine reaction, the drug company will usually pay for it.
          Titre testing is great, I have no problem with it – but sadly it’s useless for leptospirosis because the immunity to leptospires doesn’t generate significant levels of antibodies; it’s a T-cell based response, which cannot (as yet) be reliably measured. We know the vaccine is effective at what it does, because it’s been demonstrated through challenge, but there’s no simple test for immunity.

  4. Check before Annual Boosters – Unfortunately there are some unscrupulous vets who will advise on and administer annual vaccinations when they are not needed. Depending on the manufacturer of the Vaccine boosters should only be administered once every three years. Be sure to check and challenge your vet over this!!

    1. Absolutely correct – most dogs and cats do not require distemper, parvovirus or canine adenovirus any more often than every three years.
      However, it’s important to remember that some vaccines – such as Leptospirosis or parainfluenza – do not last significantly longer than a year, and for these components, annual revaccination is required to maintain effectiveness.

  5. Why give lepto 4 when 50% of the strains covered by this ‘new’ vaccine aren’t rampant or even partial to the UK’s climate? why give this vaccine when most cases can be rectified by antibiotics? This vaccine is killing animals, my dog developed 5-6 grand mal seizures daily, even on a high dose of pheno etc, he developed bladder stones and kidney failure, all within a month of this drug. Find me a vet who would call these complications a coincidence, because that’s what the majority of vets are doing.

    if you must vaccinate, use L2.

    1. I did discuss those points in the blog, you might find it useful to follow some of the links to the original data.
      According to the best data we have, about 1 in 20 dogs in the UK has been exposed to one of the new strains (Bratislava), whether or not the bacteria like it here, they are living here quite happily!
      Unfortunately, the infection cannot be simply “rectified” with antibiotics – even with antibiotic treatment, about 60% of infected dogs are reported to die.
      While I’m really sorry that your dog became ill, there really is a chance that it was a coincidence. It’s difficult to see how vaccination could lead directly to bladder stones, for example. Statistically speaking, the risk of an adverse reaction to the L4 vaccine is about 7 in 10,000; however, the main reason that infection is still fairly uncommon is because most dogs are vaccinated, giving some level of herd immunity and restricting the transmission of the bacteria. Unfortunately, the more scare stories about vaccines are spread around, the higher the risk to other people’s dogs (and their families) becomes.

      1. You talk about The Dog!!!
        I have just read numerous stories about dogs’ who have died after this vaccination not “the dog”.

        I have just returned from the vet having my 3 Labradors vaccinated. I had no idea that the vaccine had changed to L4 and L2, I am now in such a quandary as to whether I should take them back in 4,weeks?
        I have been with this practice for 21 years, although I understand that they were taken over 3 years ago, totally devastated for these owners who have lost their beloved pets, but please let us have some facts about these new vaccines?

        1. I was answering sg’s question about the side effects that her specific dog developed.
          Yes, there are lots of stories about dogs that have died – however, I have never seen such a reaction, and nor have the vast majority of the vets I’ve spoken to. The VMD (the medicines regulator) is unaware of an epidemic of serious side effects related to the L4 vaccine.
          If you want reliable facts, take a look at the links in the article, and be cautious of uncurated social media groups.

        1. Unfortunately, the titre tests that can be used (and are very helpful!) for the core vaccines are useless for leptospirosis. The reason is that the protective immunity doesn’t seem to involve antibodies (which may be present in an unprotected dog, or absent in a protected one, or vice versa!) but cell mediated immunity. In a natural infection, antibodies are produced so can be used to detect infection, but they aren’t terribly protective.

      2. There is no research done on canine lepto in UK. The only one I could find, and I have access to a lot of research paper, is one from 1991 done on stray dogs witch actually shows the contrary of what you are saying. There is no evidence anywhere that anyone is keeping track of how many dogs died in the UK of lepto, so I guess the number is not so high is it if none find it worth to bother. If you know of any research papers proving that lepto is prevalent in UK (please do not share research done by the medication company which makes money from the vaccine, but independent research) then please share with us.

        1. There are some more recent papers. For example:
          Ball, C., Dawson, S., Williams, N.(2014) “Leptospira cases and vaccination habits within UK vet-visiting dogs” Veterinary Record 174, 278.
          Who found that “We demonstrate that canine Leptospira infections are present in the UK despite vaccine availability, and that dogs are dying as a result of such infections”

          Taylor, C. (2019) “Canine leptospirosis in the UK and Ireland” Veterinary Ireland Journal 9:5This article covers the presentation, diagnosis and treatment of leptospirosis in dogs, and also discusses the limitations of the current tests and the risk of false negatives.

          Sant’Anna, R., Vieiraa, A.S., Oliveirab and Lilenbauma, W. (2019) “Asymptomatic leptospiral infection is associated with canine chronic kidney disease” Comparative Immunology, Microbiology and Infectious Diseases 62
          Have a new perspective on the possible side effects of asymptomatic leptospire carriage.

  6. My Labrador pup was given dhp and L2 at 71/2 weeks the note on the vaccine card said between 2-4 weeks for the next I made the appointment for 2weeks later and the vet said she should have L4 due to us living by a lake she also said we need another dhp in 2 weeks and the second L4 in 4 weeks is this right will I ever be able to put my puppy down to walk in the park my 6yr old lab had one shot at 8 and one at 10 wait 10 days then she could be walked any advice

    1. It depends on the exact brands, but yes, the time interval between 1st and 2nd L4 is different to that for L2 – and for many brands it does, sadly, mean an extra trip.

  7. Our puppies breeder had them vaccinated with DHP and L2 after 7 and a half weeks. After we picked her up at 8 weeks we took her o the vets after a couple of days for an initial check up and the vet recommended giving her the L4 even though it was only 1 week after having the L2. We have been told to go back in 4 weeks for the top up of L4 but in the mean time we can take the our puppy out a week after the first L4 vaccination.

    I’m nervous of taking her out before she is fully vaccinated and am wondering if we can go back to the L2 vaccination after reading the risks of L4.

    Is it too late to go back to the L2 once she has had the L4?


    1. The difference in risk between the two really isn’t that dramatic, and the additional cover provided could be invaluable. Remember, we never hear about all the millions of dogs given L4 who DON’T get side effects and DON’T get Lepto because they’re protected, only the very tiny number who do.
      However, if you think that the risk is too high, it’s absolutely your decision, and it is the responsible thing to do to make sure your dog is protect against the other two strains. The good news is that yes, you can convert back to the L2 from the L4, because the L4 contains both the strains in the L2.

  8. Before we picked our new puppy up he was given his first L4 vaccine at 10 weeks. I contacted our local vet who only uses the L2 and they said it’s fine for him to have the second vaccination of L2 as it is compatible with the first L4 vaccine; is this correct? He is due to have to second jab in just over a week (12 weeks old) and I just want to make sure he will be fully covered.

    1. Yes, the L2 can boost the L4 (because L4 contains the 2 components in L2); but you won’t get the protection from the other 2 elements.

  9. I’ve had this discussion for the last 2 years with my vet, and every year I’m persuaded by the vet (honestly it feels more like being forced) to have L4. This doesn’t sit well with me at all, I know of and have met several chihuahua owners who have lost dogs after vaccinations with L4, can I ask my vet to only use L2 or will I have to find another vet who will do it? I asked once if I could order L2 in for my Chi and was told I’d have to buy a whole tray for around £150.
    I’m happy to pay for a prescription and order it myself, even though I pay for vaccinations and parasite prevention through a care package. I feel like I should have the final decision, as the owner, about my dog’s vaccinations. Or am I wrong? How is the best way to ask this of my vet? I haven’t succeeded so far.

    1. An open discussion about the risks and benefits is the best way forward. However, the vaccine is a prescription only medicine, and strictly you have no legal right to demand a product that your vet believes to be less effective. It sounds as if they have offered to source it, but that the cost was something you were unwilling to bear (which is fair enough).
      It is possible to order the L2 from some veterinary dispensing pharmacies – although you will have to pay for refrigerated delivery. If your vet was willing to order a tray of L2 in for you in house, then they cannot legally refuse to issue you a prescription for the same drug. Just make sure you choose a reliable and reputable UK-based pharmacy or dispensary that is properly inspected and regulated!

  10. I order the L2 vaccine from viovet – it’s not that expensive at all. You need a prescription from your vet to order.

  11. I got a Jack Russell terrier. I didn’t know anything about L4 so she got the first dose two weeks ago. Reading my papers, I realised I need to repeat same dose again four weeks later. My questions are:
    – is it necessary to repeat dose?
    – what about if I do a titer test first to see if second dose is necessary?
    – If I have to give her second dose, it would be better to wait more than four weeks so her body will have more time to recover from the first dose?
    Your opinion and advice would be very useful.
    Many thanks.

    1. Hi Paloma, thanks for getting in touch. With initial vaccinations, two doses are usually required in order to be effective to start the course. Following on from that, your dog would need ‘booster’ vaccinations at varying intervals throughout their life to maintain immunity. I’d recommend contacting your vet regarding the second dose of L4, when it can be given etc. as it can vary depending on the manufacturer of the vaccine, so your vet will be best placed to advise.

  12. Hi my 5 month old cockapoo had his 2 injection of leptospirosis 4 last night within a minute at the vets he started crying in pain. We took him home he looks very depressed and keeps crying every now and then especially when he moves or gets up. He is led down alot which is totally out of character for him and he has not eaten any breakfast . My concerns are will he get over this or will it get worse and also if he does get over this what do I do in a year’s time after a reaction like this do I just get leptospirosis 2 done as he had an awful reaction to leptospirosis 4?
    Any help with this decision would help.

    1. The Lepto vaccine does sting, but lasting side effects are very rare. Many animals are a little off colour for 24-48 hours after a vaccine – this is because the vaccine is stimulating an immune response (it has to to work), which often makes them a bit lethargic. I would be very surprised if he didn’t bounce back after a day or so (although there might be a small swelling at the injection site that takes a few days to go down). I would not say that this was a reason not to vaccinate next year, assuming the effects resolve as quickly as they usually do, because Lepto infection is much more unpleasant and very unlikely to resolve rapidly and harmlessly on its own.
      If the effects are at all prolonged, though, do make an appointment to get him checked out by your vet – a very small number of dogs do develop more serious side effects, although they’re very rarely dangerous.

  13. I have concerns about the L4. Breeder says stay away from it, yet vet says I should do. I trust my vet, but something not sitting right with L4. I think I will compromise & give L2 whilst a puppy & when comes to annual vacs change to L4 – he’ll be bigger & stronger by then & also gives me an extra year to research. Is it ok to start the vacs off again at the annual booster – i.e change to L4? I don’t think I’ll have any choice but to do that – as insurance says has to have the annual boosters

    1. The problem with the L4 vaccine is one of perception, rather than safety, as far as we can tell from actual evidence (rather than rumour). Any vaccine can have side effects, of course; mild side effects do seem to be more likely the first few times a vaccine is given than subsequent ones, but this again might be anecdote, I’m not aware of any actual evidence on this!
      I would certainly say to use L2 rather than no Lepto vaccination; however, bear in mind that boosting L2 with L4 does not give your dog immunity to the 2 additional strains of Lepto in the L4, so would not be in accordance with the manufacturer’s license or presumably the insurance company’s terms (although you’d have to check that with them). The only way to do so would be to restart the lepto vaccination course with 2 injections, 4 weeks apart, when you decide to change over to L4.
      Hope that helps!

  14. We are bringing home our 8 week old cavapoo on the 5th September. The breeder’s vet gave her the first L2 injection on 29th August. We live an hour away from the breeder and will be using our local vet Vets4Pets for future injections, unfortunately they use the L4 injection.
    We have decided to go back to the breeder’s vet for the 2nd injection, thereafter using our local vet. Who, I might say, have an excellent reputation.

  15. We have a labrador retriever, our 2nd one from the same breeder who has been established for over 50 years. They stressed to us that we should stick to Lepto 2 and not Lepto 4. Today, our dog has had a Lepto2 booster, he is 15 months old and very healthy. Do not be strongly persuadedy to upgrade to Lepto 4, do some research and make your own judgment. We have, and we certainly would not take the risk which is what it all boils down to.

    1. The L4 protects against diseases that are present in the UK and kill dogs in the UK, which are not included in the L2. That said, these strains (or serovars) do appear to be less common than the other two. It is a very safe drug compared to, for example, paracetamol in humans, but there is some evidence suggesting there are slightly more adverse reactions (although these are mainly minor) than the older vaccine. So yes, definitely do your research, but remember to include unbiased, evidence-based and peer-reviewed sources, not just rumour and anecdote.

      1. Yes please do include dear David Harris some unbiased, evidence based research on how many dogs have dies of lepto in the UK in the past few years. Please do. We want to see your evidence

        1. If you follow the links in the text, you’ll find the original research that the article is based on.

  16. Is the Lepto 2/4 vaccine Live or dead bacteria, if we are having multiple dogs vaccinated over a span of say one to two months does this leave the adult dogs and pups not yet vaccinated exposed to contracting the disease due to the others shedding it, we had a couple of dogs react negatively to the L4 three yrs ago, after having L2 with no real side effects and so have stayed away from this vaccine since but feel it in the dogs interest to get them covered, we just want to do it safely and wisely. Our Vets are brilliant and will support us by providing L2 if this is what we choose but have also been good in giving us reassurance if we wanted to explore L4 again with some of the dogs, with so much worrying information out there there is a temptation to just not have either but i know if the disease is contracted its life threatening, we also advise new puppy owners on this, mainly saying to them to ask their vets advice but would be nice to have some answers to the above Thank you for your time

    1. No problem, thanks for commenting! Both the L2 and L4 vaccines are dead and do not contain any live bacteria; as a result, shedding isn’t going to be a problem with these products.

  17. Sorry but this article is very strongly worded in the ‘Pro’ vaccinate, in my opinion. Words like “‘supposed’ to have died” are not helpful. Also, the major study in Scotland was, I believe on strays so you could, (using similar logic to that in your article) posit that strays never had a vaccination for lepto and if they have the disease seem to have survived – making lepto not always deadly and EXTREMELY rare.
    Also suggesting that as 5% of strays were infected and excreting the virus poses a 5% risk to all dogs is great example of lies, damn lies & statistics. Is your dog hanging round with THIS sample of strays in Scotland?

    The truth is that leptospirosis is a VERY, VERY rare disease in the UK, (and in Europe). Humans can contract it too BTW, (every heard of anyone taken ill with a dose?). Humans are not advised, (in all but the most extreme environments) to vaccinate against it – it’s too rare Vs the risk of reaction to the vaccine.
    Does your dog spend a lot of time around farms and farm animals? Do they like stale or stagnant fresh, (not salt) water? These are the at risk situations.
    Learn the symptoms of lepto, (similar to flu) and get your pup off the vet for some antibiotics (which do a great job of killing lepto) if you suspect a case.
    BTW L2 or L4? L2 cover 2 ‘strains’ and L4 covers 4 ‘strains’ of lepto. There are about 200, (possibly more) known ‘strains’ of lepto and at best your protected for (the most common? difficult to tell as ITS SO RARE) 2 or 4 with all the side effects, (deaths) this entails OR don’t take your pal near stagnant water or farm animals and know the symptoms of this VERY rare disease.
    Titre testing for DHP is a much better idea that dosing every three years. You’ve vet shouldn’t complain about this as the titre test, (blood test to check for the presence of protection) costs about the same as the DHP booster itself.

    In short, don’t panic lepto in dogs, (and humans) is VERY RARE. Would you vaccinate your child for lepto if they crawl around the grass near ponds? I can happen tho, so know the symptoms and act.

    1. The main reason lepto infection is rare is because most dogs are vaccinated, so that’s something of a circular argument! And yes, in general I am pro-vaccination because in general the evidence supports it as a way of improving animal health and welfare. Meningitis in humans is also pretty rare, but the meningococcal vaccine is still generally accepted as a good thing…
      I have seen dogs (and humans, as it happens) with clinical leptospirosis and antibiotic treatment is far less effective than you suggest – 20% mortality figures are usually quoted despite treatment – hardly doing “a great job of killing lepto”.
      Leptospirosis is present in the UK (three of the four serovars in the L4 vaccine) and it does kill dogs. Not all dogs, of course, but far more than any actual evidence suggests have been killed by the vaccines.
      One one thing we do agree though – titre testing is a great innovation, and I absolutely support its use. For distemper/hepatitis/parvo, it’s a great way to tell whether your dog is one of the lucky ones with multi-year immunity, or not.

  18. My 3yo pup had the first dose of his first ever L4 vaccine (previously had L2) and was due the booster 4 weeks later, however I missed the appointment and have only realised now – week and a half later.

    The front desk lady at the vet’s said he’ll have to start over, and the Nobivac information sheet does specify a 4 week interval.

    I’m very worried about essentially giving him 50% more in a very short space of time by restarting the vaccine. Was wondering if restarting but with L2 could be safer. On the other hand, ha hasn’t had a reaction after the initial dose of L4. Would really appreciate your thoughts before I speak to my vet.

    1. To be honest, it’s very hard to know what’s the best thing to do in this situation. I think the probability is that even with 3 vaccines relatively close together, there won’t be a problem – but as with any medicine, it’s impossible to guarantee that. I’d be include to chat with one of the vets about it, rather than the receptionist; personally, I would probably restart the vaccine with both L4 components, but this is entirely your call. The thing with the L4 is that its a dead vaccine, which means that the immune system doesn’t respond as powerfully to it as to the live vaccine components – this is why 2 doses a set period apart are so important.

  19. I’ve got 4 dogs all are foreign rescues! 2 are coming up for their annual vaccinations (they are 2 1/2). One dog is a lab x lurcher and she had a severe site reaction from the vaccination last time so I didnt take either of them back for the follow up lepto that was due 4 weeks after the initial vaccinations.
    My question is – I would like my dogs titre tested to see exactly what vaccinations they now require. Is it ok to ask my vet to titre test first? Or should I just go ahead and get the vaccinations but stick to Lepto 2…

    1. I think if one of them has had an unusually bad site reaction then a titre test might be a good idea. However, remember you can’t do a titre test for Lepto (the results are meaningless because the vaccine doesn’t work by generating antibodies but a cell mediated response). It’s impossible to know which component to the combined vaccine your dog reacted to, but a titre test will let you know which (if any) of the initial distemper, parvo and hepatitis components have taken. Regarding the Lepto component, if they only had the initial dose not a second one, they have no induced immunity to leptospirosis at all – because it’s a dead vaccine, 2 doses are needed, so they will need to restart the lepto vaccine schedule from scratch

        1. I’m afraid you are incorrect. The immune system responds to the vaccine and dogs develop some degree of immunity – as I said in the article, vaccination against leptospires is good at reducing the severity of infection and very good art reducing carriage. This is one aspect of immunity. While I wish it did prevent all infections, sadly, no-one’s managed to produce a vaccine that does that yet, so we’ll have to settle for one that means that dogs if infected are less likely to die and less likely to pass the bacteria on.

  20. Hi – I found your article really informative. My puppy had the Lepto 4 vax on Monday 21 October – that’s his very final injection. When will it be safe to take him out for a walk … my vet said 3 weeks, he will then be 16 weeks old, is that correct or will he be safe to walk earlier than this?

    1. 3 weeks is usually about right – how long it takes immunity to become firmly established after the second vaccine is variable, but listed by the manufacturer as 3 weeks – hence the waiting period!

  21. My dog’s first injections were L4 – her one year booster was an L2 (the vet did not check her paperwork before injecting her). He then said we will have to restart the vaccination as if she was a puppy and another injection would be needed 2 weeks later. Or we could get another L4 booster 2 weeks later.

    He then phoned me and said no further injection is needed as the L2 will boost the 2 of the 4 in L4. Does anyone know if this is the case? After doing some research it would be good to avoid having an additional L4 if we could but obviously want to make sure my dog is protected.

    1. Essentially, the L2 contains 2 of the 3 common serovars (versions) of Leptospira found in the UK (Icterohaemorrhagiae and Canicola); the L4 contains the third (Bratislava). The fourth strain (Grippotyphosa) has not been widely recognised as present in the UK at this time.
      Theoretically, the L4 should boost the Icterohaemorrhagiae and Canicola. However, you are not protecting against Bratislava, which is present in the UK. As far as we know, there’s very little cross-protection between serovars (so being protected against one is unlikely to protect against another), and unlike some of the other vaccines, the duration of immunity is very short.
      Ultimately, it is up to you and your vet to decide what risk your dog is at – with the L2 vaccine boosted, your dog should have about 2/3 protection against UK strains, the question is whether you want to cover for the third.
      The only additional comment I’d make is that if you intend to take your dog to the mainland EU, then I would strongly advise the L4, as the Gryppotyphosa strain is very common in Germany in particular.

  22. Of course because all veterinary members of staff are made of money and call your dog in for its annual booster just so they can go buy a new car. Medications all have risks, they could have underlying conditions which causes these deaths rather than the vaccine. Of course if you was the owner and got the dogs post mortems then perhaps you would have valid information that it was the vaccine that caused the issue. I hope no immuno compromised dogs get ill from the unvaccinated dogs on your advise as that would be very sad.

  23. I would like to ask a question regarding immunity for puppies from the mother and how long this lasts please? Thanks

    1. Unfortunately, there is no useful test for Leptospira immunity – antibodies are short-lived and levels do not correlate with protection. It is likely that puppies pick up some immunity to Lepto from their mother – but this is not certain, and there is very little research. This makes sense when you consider that the only reliable way to demonstrate maternal protection would be to deliberately infect healthy puppies with lepto and see at what age they started to die. Clearly this wouldn’t be an ethical experiment and to the best of my knowledge, has never been performed.
      In any case, the minimum age for vaccination with both the L2 and L4 vaccines is 6 weeks, to ensure that they are immune competent and able to respond appropriately to the vaccine.

  24. Both my 8wk French Bulldog girls were done last Tuesday & are fine. 1 is with her new owner since yesterday & will be coming back to me for her 2nd vaccine. I have owned horses for 40yrs & none ever had a reaction to the flu jab, but I have known others react. Didn’t stop me having mine done.

  25. We use the L4 on our Cockapoo girl and will continue to ensure the L4 is given to all dogs we own. Our girl loves swimming and is always in water as we live in a rural area. Vaccines keep diseases at bay which are significantly worse than a quick scratch at the vets. It’s our duty as responsible owners to protect our animals and give them the best start and ongoing care. There are always unfortunate cases where things go wrong but this is vastly outweighed by the amount of successful vaccinations done every day.

    Great informative article!

  26. What a great article and also excellent evidence informed comments. As a healthcare professional, we are guided by the data and evidence. That’s all we have. No data without stories and no stories without data. I could have the flu jab tomorrow and unfortunately have a very rare reaction to it. Unlikely, but I could. Same goes for lepto. Would you go to the doctor and argue about their decision making?

  27. My 3-year-old German Shepherd had a seizure after changing from the L2 to L4 and some mucus diarrhea. Luckily just one seizure (fingers crossed still early days) and the diarrhea has now cleared up. His vets have noted the reaction on his records and sent a report. I do think reactions are greater than is being reported for the L4. Everyone knows someone whose dog has had a reaction to the L4. Sadly due to this all vaccinations are now coming under suspicion. My research since my dogs reaction is now making me question the L2 – which he has had without issue. Many people I know are testing and not vaccinating at all. So far there has been no rise in cases of illness as a result. What the L4 has done in conjunction with vets refusing to acknowledge a problem – is undermine vaccination and the profession. These are just my thoughts after talking to people. Will I now vaccinate Milo? will I vaccinate future dogs? Right now I do not know what to do for the best.

    1. Unfortunately, there’s no test for immunity to leptospirosis.
      If it helps, I’ve never seen a reaction to L4 except for the occasional and temporary swelling at the injection site; the vast majority of vets I’ve spoken to say the same thing. So either all these people who have had reaction haven’t done the sensible thing, that you have, and told their vets, or there’s something else going on – and I’m afraid that mass hysteria about vaccines is nothing new.

  28. Hi David, I recently brought my Golden Doodle puppy home from the breeder. She was very much against any lepto vaccine especially the Lepto 4 and suggested that vaccinations are more effective from 12 weeks rather than 8 weeks. I have chosen to vaccinate my puppy at 10 weeks, as a compromise as I think it is important for puppy to get out and socialise, although I will be doing this by carrying her so she discovers new sights and sounds. I am so torn in regards to the lepto 4 vaccine and getting quite distressed, my vet recommends it and has never seen an adverse reaction buy it conflicts with my breeders advice. I have read that reactions are more common in golden retrievers which is why I am so undecided.

    1. I’ve never seen a serious reaction to L4 in practice; while I’m not saying they can’t happen, I think they’re really rare. The figures are very reassuring! I’m not aware of any data suggesting that Golden retrievers are actually at higher risk, although it is possible – however, I do know that a lot of breeders (of all sorts of breeds) say that their dogs are at increased risk. I think there’s a lot of Chinese whispers going on here, sadly, and it’s not backed up by the facts that we have.
      The last thing I’d point out is that your breeder is an expert in getting dog’s pregnant and raising them to a couple of months old. Your vet is an expert in keeping them healthy and treating them when they’re ill.
      I hope that helps!

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