Overdue pets usually need revaccination, not a full restart
Bottom line
Scott Weese’s latest Worms & Germs post tackles a common practice question: what to do when a dog or cat is overdue for vaccines. His bottom line is straightforward: in most cases, don’t restart the series. Revaccinate the overdue animal as you normally would, while recognizing that rabies can be different because local regulations, travel rules, and public health policies may not line up neatly with immunology. Weese notes that an overdue pet is still usually best managed with a booster now, but some jurisdictions may only treat that rabies booster as valid for one year before the animal can return to a three-year schedule. (wormsandgermsblog.com)
Why it matters: For veterinary teams, this is a practical reminder that overdue does not automatically mean unprotected, and it doesn’t necessarily mean starting over. That aligns with broader guidance from AAHA, which says the benefits of vaccinating overdue or unknown-status dogs generally outweigh the risks, and with WSAVA’s emphasis on evidence-based revaccination and selective use of serologic testing for some core antigens. The key exception is rabies: clinics need to pair medical decision-making with a clear understanding of state, provincial, or travel-specific rules, because compliance consequences can fall on both practices and pet parents. (aaha.org)
What to watch: Expect more discussion around how practices document overdue rabies boosters, counsel pet parents on legal risk, and use newer guidance tools such as the Ontario Animal Health Network vaccination interval resources. (wormsandgermsblog.com)
A new Worms & Germs post from infectious disease specialist Scott Weese puts a spotlight on a deceptively simple exam-room question: what should veterinarians do when a dog or cat is overdue for vaccination? Published September 28, 2026, the post argues that, for most overdue companion animals, the answer is not to restart a vaccine series, but to revaccinate based on normal principles while separating immunologic protection from regulatory treatment, especially for rabies. (wormsandgermsblog.com)
That distinction matters because overdue vaccination has long been an area where evidence, label language, habit, and legal rules don’t always align. Weese frames the issue around the reality that vaccine recommendations in companion animals often blend direct evidence with extrapolation and expert opinion. His position is that immunity does not suddenly disappear the day after a due date passes, particularly for core vaccines with established duration of immunity, but public health rules may still define an overdue rabies patient more narrowly. (wormsandgermsblog.com)
The broader guideline landscape supports much of that approach. AAHA’s canine vaccination guidance says that when vaccines are overdue or status is unknown, the benefits of vaccinating generally outweigh the risks and offers a simple rule of thumb: when in doubt, vaccinate. AAHA also notes that its canine guidance was updated in 2024 to classify leptospirosis as a recommended core vaccine for all dogs, underscoring how vaccine risk assessment continues to evolve. On the feline side, the 2020 AAHA/AAFP guidelines stress individualized risk assessment and identify core vaccines for cats with unknown histories, rather than suggesting a blanket restart mentality. (aaha.org)
Weese’s most practical nuance is around rabies. In his post, he says he would have “absolutely no concern” that an overdue dog revaccinated today would be protected for at least the next three years, but he also warns that some regulators may only consider that booster valid for one year. He adds that some jurisdictions allow more flexibility based on the prior record or a short lapse, while others remain strict enough that even a one-day delay can disrupt a three-year designation, particularly for border crossing or overseas travel. His advice is to vaccinate now, then think carefully about whether a one-year booster is prudent to avoid quarantine, travel disruption, or compliance problems. (wormsandgermsblog.com)
Industry and expert guidance adds context, even if it stops short of addressing every overdue scenario directly. WSAVA’s 2024 vaccination guidelines reinforce that local regulations should take priority for rabies revaccination intervals and note that serological testing can help with some vaccination-related decisions for core viral antigens, though not as a universal substitute for revaccination. That gives practices another tool for selected cases, particularly when medical complexity or prior adverse events make routine revaccination less straightforward. (wsava.org)
Why it matters: For veterinary professionals, the message is less about a new rule than about cleaner clinical reasoning and better client communication. Overdue animals are common, and defaulting to “start over” can add cost, inconvenience, and confusion without clear immunologic justification. At the same time, rabies remains a compliance-sensitive exception where the medical answer and the legal answer may differ. That means clinics should have a consistent protocol for documenting prior vaccine history, checking jurisdiction-specific rabies rules, and explaining to pet parents that a booster may be medically adequate today but still carry legal caveats depending on where the animal lives or travels. (wormsandgermsblog.com)
What to watch: This looks like the start of a broader educational series from Weese, and he points readers to a paired Ontario Animal Health Network resource on vaccination timing and intervals in dogs and cats. The bigger near-term question for practices is whether more regulators, boarding facilities, insurers, and international travel authorities will adopt more flexible interpretations for overdue rabies boosters, or continue to rely on rigid interval-based rules that can outlast the science. (wormsandgermsblog.com)