An evidence-based guide to the leptospirosis vaccine for dogs — who needs it, how long protection lasts, what the AAHA-ACVIM reclassification means, and when veterinarians use caution.

Leptospirosis is a potentially fatal bacterial disease that can cause acute kidney failure and liver damage in dogs — and it is zoonotic, meaning infected dogs can transmit it to people. Once considered a rural disease of large-breed dogs, leptospirosis is increasingly diagnosed in urban and suburban pets. The vaccine has changed too: newer quadrivalent formulations have a better safety profile than older products, and the American College of Veterinary Internal Medicine (ACVIM) and the American Animal Hospital Association (AAHA) now classify leptospirosis vaccination as core for all dogs. In October 2023, ACVIM issued an updated consensus statement recommending annual leptospirosis vaccination for all dogs over 12 weeks of age regardless of breed, geography, or lifestyle. AAHA subsequently recategorized leptospirosis as a core vaccine in its 2024 update to the 2022 Canine Vaccination Guidelines.

This article explains what leptospirosis is, how the vaccine works, what side effects to expect, how long immunity lasts, and how to decide whether the vaccine fits your dog.

Quick answer

The leptospirosis vaccine is an inactivated bacterin that protects dogs against four common disease-causing serovars: Canicola, Icterohaemorrhagiae, Grippotyphosa, and Pomona. It requires an initial two-dose series given 2–4 weeks apart, followed by annual boosters. Immunity lasts approximately 12 months — it does not provide multi-year protection like some viral vaccines.

AAHA and ACVIM now classify leptospirosis vaccination as core for all dogs, regardless of lifestyle or geography. The AVMA states that "all dogs are at risk of leptospirosis, regardless of age, breed, lifestyle, geographic location, time of year, and other factors." The CDC confirms that "almost every dog is at risk of leptospirosis, whether they live in the country, suburbs, or city."

What leptospirosis is and why the risk has changed

Leptospirosis is caused by spirochete bacteria of the genus Leptospira. Dogs become infected when mucous membranes (mouth, nose, eyes) or broken skin come into contact with urine from infected animals, or with contaminated water, soil, or bedding. Common carriers include raccoons, skunks, opossums, rats, cows, and pigs.

The disease attacks the kidneys and liver. Signs can be vague at first — fever, lethargy, reduced appetite — and progress to vomiting, dehydration, back pain from kidney inflammation, jaundice, and in severe cases, acute kidney failure or death. The AKC Canine Health Foundation reports that over 25% of infected dogs in a Chicago-area study did not survive.

Why urban and suburban dogs are now at risk

Leptospirosis was once considered a disease of rural dogs exposed to livestock or wildlife. That assumption no longer holds:

Urban wildlife (rats, raccoons, opossums) are increasingly common carriers as habitat is lost to development.
A 2026 dvm360 lecture by Jane Sykes, BVSc, DACVIM, traced a major Los Angeles outbreak in which affected dogs were either completely unvaccinated or had received only one dose without the booster. Many affected practices did not even carry the vaccine.
AKC Canine Health Foundation research found that urban dogs in Canada were more likely to test positive than rural dogs.
Outbreaks have been linked to standing water after floods, heavy rain, and snowmelt.

Dogs not vaccinated for leptospirosis were 20 times more likely to get sick in one study, and young, male, and small-breed dogs were at highest risk.

How the leptospirosis vaccine works

Current canine leptospirosis vaccines are inactivated bacterins — they contain killed Leptospira bacterial components, not live organisms. They cannot cause leptospirosis infection.

Most modern products are quadrivalent, covering four serovars:

Serovar	Primary reservoir	What it targets in dogs
Canicola	Dogs	Kidney disease
Icterohaemorrhagiae	Rats	Liver disease
Grippotyphosa	Wildlife (raccoons, skunks)	Kidney and liver disease
Pomona	Livestock (cows, pigs)	Severe kidney and liver disease

Cross-protection between serovars is limited. A dog vaccinated against Canicola and Icterohaemorrhagiae alone is not well-protected against Grippotyphosa or Pomona. This is why AAHA and UC Davis recommend quadrivalent (4-serovar) products whenever possible.

Vaccination schedule

Step	Timing	Notes
First dose	12 weeks of age or older (per AAHA guidelines; some product labels allow as early as 8 weeks)	Puppies can receive the first dose alongside other puppy vaccines. AAHA recommends starting at 12 weeks; some practices administer the first dose earlier per label.
Second dose (booster)	2–4 weeks after the first dose	Protection is not reliable until the second dose is complete. Dogs with only one dose are still vulnerable.
Annual booster	Every 12 months thereafter	Duration of immunity is approximately 12 months. Some products have label claims up to 15 months, but annual revaccination is the standard recommendation.

If a dog goes more than 18 months without a booster, many veterinarians restart the two-dose series to rebuild protection. There is no multi-year leptospirosis vaccine — unlike rabies or distemper, this one must be given annually.

The initial two-dose requirement means there is a gap of several weeks before a dog is fully protected. A dog that acquires leptospirosis before the second dose is not considered immunized.

How long protection lasts

Challenge studies by vaccine manufacturers show protective immunity lasting approximately 12 months. A published study found 15-month duration of immunity for serovar Grippotyphosa. However, antibody titers (as measured by the microscopic agglutination test, or MAT) are unreliable indicators of protection — dogs with low or undetectable titers can still be protected through cellular immune memory, and dogs with high titers are not guaranteed protection. The MAT is not useful for deciding whether a dog needs a booster.

Because antibody levels decline steadily and the vaccine does not induce long-lived immunity like viral vaccines do, annual revaccination is required to maintain protection. Missing a year creates a real gap in coverage.

Side effects

Modern leptospirosis vaccines have a significantly improved safety profile compared to products from the 1990s and 2000s. Older formulations were associated with higher rates of acute allergic reactions — especially hives, facial swelling, and in rare cases anaphylaxis — particularly in small-breed dogs such as Dachshunds and Chihuahuas.

AAHA data report fewer than 53 adverse events per 10,000 doses for leptospiral vaccines, and most are minor. UC Davis notes that "due to improvements in vaccine composition, reaction rates for vaccines containing Leptospira now approximate those for other core vaccines."

Common (mild, self-limiting, 24–48 hours):

Soreness or mild swelling at the injection site
Low-grade fever
Mild lethargy or reduced appetite

Less common (contact your veterinarian):

Vomiting or diarrhea lasting more than 48 hours
Hives or facial swelling
Limping
Difficulty breathing

Rare (requires immediate veterinary attention):

Anaphylaxis (collapse, difficulty breathing)

If your dog has previously reacted to a leptospirosis vaccine, tell your veterinarian. Pre-medication with an antihistamine or anti-inflammatory may be recommended, and the dog should be monitored for 10–15 minutes after the injection. UC Davis notes that reaction risk tends to decrease with age.

The vaccine should not be given to pregnant dogs, or to dogs sensitive to specific preservatives (amphotericin or gentamycin) used in some formulations.

What this vaccine does not do

The leptospirosis vaccine does not provide complete protection against all Leptospira serovars. Multiple serovars exist beyond the four covered in current vaccines, and natural exposure can still cause illness — though vaccinated dogs tend to have milder symptoms and are less likely to shed bacteria in their urine. The CDC states: "The vaccine does not provide 100% protection because there are many different strains of the bacteria, and it does not cover all of them."

The vaccine also does not treat an existing leptospirosis infection. If a dog is already sick, the treatment is antibiotics (typically doxycycline or penicillin-based therapy) and supportive care, not vaccination.

When veterinarians may use caution

Situation	Reason for caution
Prior severe vaccine reaction	Pre-medication and post-injection monitoring may be appropriate. A different vaccine product or schedule may be discussed.
Dog is currently ill	Vaccination is generally deferred until the dog has recovered, to avoid confusing illness with vaccine side effects.
Pregnant dog	Most leptospirosis vaccines are not labeled for use in pregnant dogs.
Very small breed with prior reaction history	Though newer vaccines have improved, small-breed dogs historically had higher reaction rates. Monitoring is warranted.

These are caution situations, not automatic reasons to skip the vaccine. The risk of leptospirosis — which can be fatal — should be weighed against the risk of a vaccine reaction in consultation with the attending veterinarian.

What to ask your veterinarian

Is the vaccine you carry quadrivalent? If it only covers two serovars (Canicola and Icterohaemorrhagiae), it may not protect against the more commonly encountered Grippotyphosa and Pomona serovars.
Have you seen lepto cases in our area recently? Local outbreaks are increasingly common in urban and suburban areas. Your vet may know about recent cases.
My dog had a reaction to a prior vaccine. Should we pre-medicate? This is especially relevant for small-breed dogs or dogs with a history of hives or facial swelling after vaccination.
Can the lepto vaccine be given the same day as other vaccines? UC Davis recommends administering lepto alongside other indicated vaccines rather than staggering them, because separating vaccines reduces the chance that all of them will be given, and there is no evidence that separation reduces reaction risk.
How long until my dog is protected after the second dose? Full protection requires both doses in the initial series.

Key points

Leptospirosis is no longer just a rural disease. Urban wildlife, standing water, and climate patterns put suburban and city dogs at risk.
Unvaccinated dogs are approximately 20 times more likely to develop clinical leptospirosis. Over 25% of infected dogs in one study did not survive.
AAHA and ACVIM now classify lepto vaccination as core for all dogs. Modern quadrivalent vaccines have reaction rates similar to other core vaccines.
Protection requires a two-dose initial series and annual boosters. There is no multi-year leptospirosis vaccine.
The vaccine reduces but does not eliminate risk, because it does not cover all serovars. Vaccinated dogs that are exposed tend to have milder illness and are less likely to shed bacteria.