Vaccine reactions in dogs range from mild transient discomfort to rare life-threatening anaphylaxis, with welfare implications for both the reaction itself and vaccine hesitancy that leaves dogs unprotected.
Vaccine reaction welfare sits between two harms: the rare but real welfare cost of adverse reactions and the much more common and severe welfare cost of vaccine-preventable diseases in unvaccinated dogs. Parvovirus, distemper, and leptospirosis cause severe suffering and high mortality - far exceeding the welfare costs of vaccine reactions across the population. The welfare-appropriate approach manages reaction risk through monitoring after vaccination, using 30-minute observation periods in clinic for high-risk breeds, considering titer testing to reduce unnecessary revaccination, and maintaining up-to-date vaccination for core diseases that prevent severe welfare-significant illness.