Vaccination is a veterinary practice mainstay and the foundation of good healthcare for pets, but is there anything new in vaccines? Maybe not for you, but it could be a good time to update and educate clients on vaccine safety, diseases they may be unaware of, and when to get titers. Noncore canine vaccines are tailored to lifestyle and risk—active dogs in tick-prone areas may need Lyme protection, while social or traveling dogs may benefit from Bordetella and canine influenza vaccines. Bigstock Old disease, new core vaccine Leptospirosis has leapt onto the list of core vaccines recommended for dogs, in guidelines updated in 2024 by the American Animal Hospital Association (AAHA), marking a change from its previous status as a noncore vaccine.1 The incidence of the zoonotic bacterial disease is rising in urban and suburban locales and is increasingly likely to be seen in small city dogs.2 According to the updated American College of Veterinary Internal Medicine consensus statement on leptospirosis, all dogs are at risk of the disease, regardless of signalment, geographic location, lifestyle, and time of year.3 “Since publication of the last consensus statement on leptospirosis in dogs, there has been revision of leptospiral taxonomy and advancements in typing methods, widespread use of new diagnostic tests and vaccines, and improved understanding of the epidemiology and pathophysiology of the disease,” the authors wrote in the Journal of Veterinary Internal Medicine in 2023. Globally, dogs serve as sentinels and reservoirs of leptospirosis, with important One Health implications.4 Challenges include low vaccination coverage; environmental risk factors, such as high humidity, high rainfall, and flooding, with resultant contaminated water; the presence of rodents, which are the main source of infection; underreporting of leptospirosis in regions, such as sub-Saharan Africa and South Asia; and the prevalence of stray or free-ranging dogs in some areas. As more people travel globally with their dogs, these factors are important to communicate. The World Small Animal Veterinary Association (WSAVA) designates vaccines against canine leptospirosis as core in areas where leptospirosis is prevalent in dogs, implicated serogroups are known, and appropriate vaccines are commercially available.5 A vaccine cannot be designated as “core” if it is uncertain which vaccine should be given, WSAVA guidelines state. Interestingly, French research suggests a degree of cross-protection among members of different serogroups, leaving open the possibility that commercial development of “pan-protective” vaccines could one day protect dogs against leptospirosis caused by a large majority of known pathogenic variants.6 The AAHA consensus statement recommends administering the leptospirosis vaccine annually to all dogs starting at 12 weeks of age, regardless of breed. It further recommends the vaccine should be required for dogs at daycares or boarding kennels. Historically, clients—especially those with toy or small dogs—have often been concerned the leptospirosis vaccine could cause an adverse reaction in their dog. One retrospective study in 2005 found smaller or younger dogs were more likely to experience adverse reactions to any type of vaccine.7 According to the latest AAHA canine vaccination guidelines, vaccine formulations have been altered to minimize the likelihood of such reactions,8 writing: “In the most recent large study of vaccine safety, odds of an adverse event following leptospirosis vaccination were less than with DA2PP or rabies vaccinations…. Serious anaphylactic reactions were reported no more often for dogs given leptospiral vaccines than for other vaccine antigens.” When asked about client anxiety regarding the lepto vaccine, Sarah Caddy, VetMB, PhD, DACVM, FRCVS, assistant professor at Cornell University’s Baker Institute for Animal Health, cites a retrospective study of 4.5 million vaccinated dogs over a five-year period.9 “This is a really comprehensive study, and they didn’t show lepto to have a higher rate of adverse events than the other vaccines,” Dr. Caddy says. “Figure 1 shows that if they’re five kilograms or less, they have a slightly more increased risk of an adverse event, but I think the key message to get across is that the frequency of these adverse events is really low. It is really important for owners to remember the risk of getting the disease and the severity and damage that could cause far outweighs the potential risk of an adverse event for a vaccine.” Another anecdotal belief is black and tan breeds, such as Dobermans and rottweilers, are more susceptible to adverse events, but Caddy says this is not a trend that was seen in the JAVMA study. The breeds that did show slightly higher adverse event rates were French bulldogs (55.9/10,000 visits), dachshunds (49.4/10,000 visits), and Boston terriers (44.49/10,000 visits). “That shows how important it is to do these bigger studies and the relevance of breed differences is likely limited,” Caddy says. Measures suggested by AAHA to mitigate adverse reactions include minimizing the number of different vaccines administered at a single visit and following manufacturer recommendations, such as allowing vaccines to reach room temperature prior to injection. Consider lifestyle Noncore canine vaccines remain the same and are recommended based on a dog’s lifestyle and risk factors. Active dogs in deer tick country—which continues to expand—may be candidates for the Lyme disease vaccine. Bordetella and canine influenza may be advised for dogs that travel, are boarded, go to training classes or dog parks, or compete in canine sports, including dog shows. A retrospective study by the University of Guelph’s Ontario Veterinary College (OVC), with the goal of determining the efficacy of canine Lyme disease vaccines in North America, was published in the Journal of Veterinary Internal Medicine.10 Researchers found the reported efficacies of Borrelia burgdorferi vaccines in dogs were highly variable, ranging from 50 to 100 percent, based on the results of three observational studies and 13 challenge trials. However, results showed that compared to unvaccinated dogs, vaccinated dogs had reduced odds of developing lameness, depression, pyrexia, and anorexia after exposure to B. burgdorferi. Because some of the studies reviewed had shortcomings, researchers concluded future studies should focus on larger sample sizes in field conditions. In areas where deer ticks are prevalent, or practices with clients who travel for competition or leisure to deer tick-infested areas, the Lyme vaccine may be considered core, according to AAHA guidelines. Gather this information when taking histories or during annual visits to help clients assess whether to vaccinate their dogs for Lyme disease. While rattlesnake toxoid remains on the list of noncore vaccines, it is not generally recommended. According to a 2022 AAHA statement, no published data document the efficacy of western diamondback rattlesnake (Crotalus atrox) venom toxoid in dogs. Adverse reactions, including anaphylaxis, have been reported in dogs that were vaccinated and then envenomated. The statement reads: “Veterinarians choosing to use this toxoid should be aware of the lack of peer-reviewed published data. Polyvalent antivenin therapy is an alternative to vaccination in cases of suspected rattlesnake bite.”11 Changes for cats? Feline vaccine recommendations from AAHA/AAFP12 have remained largely the same, says Lexi Botting, DVM, a clinical instructor at the University of Washington College of Veterinary Medicine. They were last updated in 2022 and advised practitioners to develop individual protocols of core and noncore vaccines for patients based on exposure risk, life stage, lifestyle, and environmental and epidemiological factors. When to titer In cases of client hesitance toward or resistance to vaccination, titers can help ensure that a previously vaccinated dog still has antibodies to the disease. Clients may choose this option if their dogs have a history of adverse response to vaccination or are suspected to have vaccine-related autoimmune disease.13 Caddy notes titers can be a great option for these clients, provided they are informed that false positives and false negatives can occur. In addition, they don’t tell the whole story of immune response to a vaccine, she says. “Those tests are just measuring antibodies. There are lots of other components of the immune system that are important, such as T-cells, and we’re not going to measure those by titer testing.” She offers another reason, though, that titers can provide important information beyond immunity status. “I was looking at vaccine antibodies in a population of dogs that came into our clinic for C-sections, and I was really surprised that 15 percent of breeding dogs didn’t have antibodies for parvo or distemper. These are dogs that don’t have maternal antibodies to pass to their pups. If you did titer testing at the point of breeding, that would have never happened. You’d have known to vaccinate again. Titer testing would tell you whether the vaccine has worked, because obviously there’s a minority of dogs where the vaccine won’t work as well as you’d hope.” Discuss with clients how vaccines are rooted in science, helping protect not only their pets but also families and the wider animal community from preventable diseases. Bigstock Vaccine resistance In one respect, at least, vaccination may have been too effective. Younger clients may have no memory of pets dying from vaccine-preventable diseases. Or clients may have experienced a cat developing an injection-site sarcoma and choose to avoid future inoculations. Lexi Botting, DVM, a clinical instructor at the University of Washington College of Veterinary Medicine, reminds clients that veterinarians are agents of public health. “We’re recommending vaccines to protect not just their pet but also their family and other animals in the area. Other animals can carry diseases, such as distemper. So even if their dog doesn’t go anywhere, if raccoons are coming around, their dog is at risk. If it’s a young, healthy dog and the owner is hesitant about vaccines for whatever reason, it’s worth having that conversation. It’s based on science and research and protecting all of our animals.” Kim Campbell Thornton has been writing about dogs, cats, wildlife, and marine life since 1985, and is a recipient of multiple awards for her articles and books from the Cat Writers Association, Dog Writers Association of America, and the American Society of Journalists and Authors. References https://www.aaha.org/resources/2022-aaha-canine-vaccination-guidelines/ Sykes JE, Francey T, Schuller S, Stoddard RA, Cowgill LD, Moore GE. Updated ACVIM consensus statement on leptospirosis in dogs. J Vet Intern Med. 2023 Nov-Dec;37(6):1966-1982. doi: 10.1111/jvim.16903. Epub 2023 Oct 20. PMID: 37861061; PMCID: PMC10658540. Sykes JE, Francey T, Schuller S, Stoddard RA, Cowgill LD, Moore GE. Updated ACVIM consensus statement on leptospirosis in dogs. J Vet Intern Med. 2023 Nov-Dec;37(6):1966-1982. doi: 10.1111/jvim.16903. Epub 2023 Oct 20. PMID: 37861061; PMCID: PMC10658540. Heydari P, Tirbandpay M, Ghasemishayan R. Systematic review of the prevalence of environmental and host-related risk factors and the zoonotic potential of leptospirosis in domestic dogs in regions impacted by environmental changes. BMC Vet Res. 2025 Oct 2;21(1):564. doi: 10.1186/s12917-025-05023-0. PMID: 41039603; PMCID: PMC12492510. https://wsava.org/wp-content/uploads/2024/04/WSAVA-Vaccination-guidelines-2024.pdf André- Fontaine, G. & Triger, L. (2018) MAT cross-reactions or vaccine cross-protection: retrospective study of 863 leptospirosis canine cases. Heliyon, 4, e00869. Moore GE, Guptill LF, Ward MP, Glickman NW, Faunt KK, Lewis HB, Glickman LT. Adverse events diagnosed within three days of vaccine administration in dogs. J Am Vet Med Assoc. 2005 Oct 1;227(7):1102-8. doi: 10.2460/javma.2005.227.1102. PMID: 16220670. Ellis J, Marziani E, Aziz C, et al. 2022 AAHA Canine Vaccination Guidelines (2024 Update). Journal of the American Animal Hospital Association. 2024 Oct;60(6):1–19. doi:10.5326/JAAHA-MS-7468 Moore, G. E., Morrison, J., Saito, E. K., Spofford, N., & Yang, M. (2023). Breed, smaller weight, and multiple injections are associated with increased adverse event reports within three days following canine vaccine administration. Journal of the American Veterinary Medical Association, 261(11), 1653-1659. Retrieved Apr 2, 2026, from https://doi.org/10.2460/javma.23.03.0181 Nadine A. Vogt, Jan M. Sargeant, Melissa C. MacKinnon, Ali M. Versluis, Efficacy of Borrelia burgdorferi vaccine in dogs in North America: A systematic review and meta-analysis, Journal of Veterinary Internal Medicine, Volume 33, Issue 1, January-February 2019, Pages 23–36, https://doi.org/10.1111/jvim.15344 Amanda J. Witsil, Raegan J. Wells, Craig Woods, Sangeeta Rao, 272 cases of rattlesnake envenomation in dogs: Demographics and treatment including safety of F(ab′)2 antivenom use in 236 patients, Toxicon, Volume 105, 2015, Pages 19-26, ISSN 0041-0101, https://doi.org/10.1016/j.toxicon.2015.08.028. https://www.aaha.org/wp-content/uploads/globalassets/02-guidelines/feline-vaccination-guidlines/resource-center/2020-aahaa-afp-feline-vaccination-guidelines.pdf Tizard IR. Adverse consequences of vaccination. Vaccines for Veterinarians. 2021:115–130.e1. doi: 10.1016/B978-0-323-68299-2.00019-8. Epub 2020 Jul 10. PMCID: PMC7348619.
