Yes, most dogs should get the leptospirosis (lepto) vaccine. As of 2024, the American Animal Hospital Association classifies it as a core vaccine, meaning it’s recommended for all dogs regardless of lifestyle. That’s a significant shift from previous guidelines, which treated it as optional based on geographic risk. The change reflects growing evidence that leptospirosis is more widespread than previously thought, showing up in urban, suburban, and rural settings alike.
What Leptospirosis Does to Dogs
Leptospirosis is caused by bacteria that attack the kidneys and liver. In the kidneys, the infection damages the tiny tubes responsible for filtering waste, leading to inflammation that can progress to permanent scarring. In the liver, the bacteria break apart the connections between cells, allowing bile to leak into the bloodstream. The disease is systemic, meaning it doesn’t stop at those two organs, but kidney and liver failure are the most common ways it becomes life-threatening.
Dogs that develop clinical leptospirosis often need intensive hospital care. One veterinary study found that affected dogs were hospitalized for an average of 11 days at a cost of roughly $5,459. Even with treatment, some dogs develop chronic kidney damage. The vaccine, by comparison, costs a fraction of that and is given once a year.
How Dogs Get Infected
The bacteria spread through the urine of infected animals, primarily wildlife like raccoons, rats, skunks, and opossums. When an infected animal urinates in a puddle, a pond, or on soil, the bacteria can survive there for weeks or months, especially in warm, wet conditions. Your dog picks it up by drinking from or walking through contaminated water, or by sniffing contaminated ground.
What surprises many owners is where infections actually happen. A study tracking an outbreak found that 66% of cases were linked to social settings like daycares or boarding facilities, and 49% were connected to dog parks. Owners also reported infections after hiking, visiting beaches, and simply walking around the neighborhood. You don’t need to live on a farm or take your dog into the wilderness for exposure to occur. Any dog that goes outside, even in a city, can encounter the bacteria.
Where Risk Is Highest
Leptospirosis has been documented across the United States, but certain regions see more cases. The Midwest, East Coast, and Southwest are more likely to produce positive test results, with some of the highest predicted rates found in Appalachian counties. Precipitation and temperature are key drivers. Areas with deciduous forests and regular rainfall create the kind of warm, moist environment where the bacteria thrive.
That said, outbreaks have been reported in cities and dry climates too. Anywhere with standing water, even a rain puddle in a parking lot, can harbor the bacteria if wildlife is present. The geographic patterns help explain why veterinary guidelines shifted toward recommending the vaccine universally rather than only in “high-risk” areas.
What the Vaccine Covers
Modern lepto vaccines are quadrivalent, meaning they protect against four bacterial groups: Canicola, Icterohaemorrhagiae, Australis, and Grippotyphosa. Older versions only covered the first two. The four-way vaccine was introduced in 2013 and provides substantially broader protection, since Australis and Grippotyphosa are among the most commonly detected strains in infected dogs. One study found Australis in 73% of confirmed cases and Grippotyphosa in 15%.
No vaccine covers every possible strain. There are many varieties of leptospirosis bacteria circulating in wildlife, and a few, like Pomona and Bratislava, aren’t included in current vaccines. Still, the four-way vaccine addresses the most common culprits and provides roughly 84% effective protection against clinical disease in experimental studies.
How Often Dogs Need It
Puppies typically receive their first lepto shot at 12 weeks of age, followed by a booster two to four weeks later. After that initial two-dose series, the vaccine is given annually. This schedule matters because immunity from the lepto vaccine doesn’t last as long as some other dog vaccines. Studies show protection holds for at least 12 to 15 months under experimental conditions, but antibody levels from the vaccine tend to be relatively low and short-lived compared to vaccines for diseases like parvovirus or distemper. Skipping a year means your dog may lose meaningful protection.
If your adult dog has never received the lepto vaccine before, they’ll also need the two-dose starter series, spaced a few weeks apart, before moving to annual boosters.
Side Effects and Safety
The lepto vaccine has a reputation for causing more reactions than some other routine vaccines, but the actual numbers are modest. A large U.S. study covering over 1.2 million dogs recorded adverse events at a rate of about 38 per 10,000 dogs vaccinated, or roughly 0.4%. The most common reactions, observed within three days of vaccination, were facial or eyelid swelling (31% of reactions), hives (21%), itching (15%), and vomiting (10%). Most of these resolve on their own or with a dose of antihistamine.
Severe allergic reactions are rare. Newer formulations of the four-way vaccine have been refined to reduce potentially allergenic compounds in the manufacturing process. Small-breed dogs tend to have slightly higher reaction rates to vaccines in general, not just lepto, likely because they receive the same dose volume as larger dogs. If your small dog has had a vaccine reaction before, your vet can take precautions like pre-treating with antihistamine or monitoring your dog in the clinic for 20 to 30 minutes afterward.
It Can Spread to People
Leptospirosis is zoonotic, meaning it passes from animals to humans. The CDC lists dogs as one of several domestic animals that carry and shed the bacteria. People become infected through contact with contaminated water, soil, or directly touching body fluids from an infected animal. An unvaccinated dog that contracts leptospirosis can shed bacteria in its urine for weeks, potentially exposing family members during that time. Vaccinating your dog isn’t just about protecting them. It reduces the risk of the bacteria entering your household.