Splitting vaccines in small dogs remains an unsettled strategy

Vaccination schedules for small dogs are getting another look, but the latest expert take is still cautious: splitting vaccines across visits may sound safer, yet there’s little evidence that it meaningfully lowers adverse-event risk, and it can create new problems if core or legally required vaccines are delayed. In a March 2026 Worms & Germs Blog post, infectious disease specialist Scott Weese said the short answer is “I don’t know, but probably not,” arguing that spacing vaccines out could help in select cases, but may also increase missed appointments, longer periods of susceptibility, and confusion around what was actually given and when. That view lines up with AAHA and WSAVA guidance, which advise against reducing vaccine dose in small dogs and note that while smaller dogs do have higher adverse-event risk, the solution is not simply giving less vaccine. (wormsandgermsblog.com)

Why it matters: For veterinary professionals, this is less about a blanket “yes” or “no” on splitting vaccines and more about risk management, scheduling, and client communication. A large JAVMA study of more than 4.6 million dogs found adverse events were recorded after 0.19% of vaccination visits, with higher rates in dogs weighing 5 kg or less and in visits where more vaccines were administered. AAHA says combination vaccines do not inherently carry more risk than single-antigen products, because the proteins most associated with reactions are often excipients or production-related proteins, not the labeled pathogen antigens. The group does, however, say reducing the number of vaccines given at one visit can be especially useful in small dogs, including delaying a noncore vaccine by about two weeks after core vaccines when clinically appropriate. (pubmed.ncbi.nlm.nih.gov)

What to watch: Expect continued discussion around individualized protocols for tiny or previously vaccine-reactive dogs, but not a guideline-backed move toward half-doses or routine splitting without case-specific justification. (wsava.org)