Sleepiness or reduced activity
A pet may be quieter for a day or two but should remain responsive and able to rest comfortably.
DOG + CAT HEALTH · AFTER VACCINATION
Vaccine reactions:
what to watch.
What can be normal for a short time, which signs deserve a call, and which symptoms require emergency veterinary care.
IN THIS GUIDEChanges that may be expected brieflySigns that need veterinary adviceGo now for breathing trouble, collapse, or rapidly worsening swellingA prior reaction changes planning—not necessarily all protectionTrusted sources
AFTER THE APPOINTMENT
Know the pet’s normal—and the red flags.
Vaccines stimulate the immune system, so brief tiredness or soreness can occur. Serious allergic reactions are uncommon, but they may develop quickly. Follow the discharge instructions from the clinic and call whenever the pet’s response seems more than mild.
Mildoften briefCallif worseningEmergencyfor breathing trouble or collapse
01 · OFTEN MILD
Changes that may be expected briefly
Mild soreness
Tenderness at the injection site, reluctance to be handled there, or a small temporary swelling can occur.
Mild fever or lower appetite
A short-lived decrease in appetite or mild fever may occur. Water intake, comfort, and trend still matter.
Important: Call the clinic if mild signs last more than a day or two, are worsening, cause significant pain, or simply worry you.
02 · CALL PROMPTLY
Signs that need veterinary advice
- Persistent vomiting or diarrhea
- Hives, marked itching, or swelling around the face, eyes, or muzzle
- A painful or enlarging injection-site swelling
- Extreme lethargy, weakness, pale gums, or refusal of food and water
- Coughing or other symptoms that are not mild and improving
Important: Do not give diphenhydramine, pain relievers, or any human medication unless a veterinarian provides the exact product and dose for this pet.
03 · EMERGENCY
Go now for breathing trouble, collapse, or rapidly worsening swelling
Difficulty breathing, collapse, blue or very pale gums, severe weakness, repeated vomiting, or rapidly progressing facial swelling may indicate anaphylaxis or another emergency. Call the veterinary hospital while leaving if it is safe to do so.
- Keep the pet quiet and minimize exertion.
- Do not force food, water, or medication.
- Bring the vaccination record and note when signs began.
- If your regular clinic is closed, use the nearest emergency veterinary hospital.
04 · FUTURE VACCINATION
A prior reaction changes planning—not necessarily all protection
- Make sure the reaction is documented in the permanent medical record.
- Ask which vaccine or product was most likely involved and whether fewer vaccines per visit, different products, premedication, or added monitoring may be appropriate.
- Do not independently skip legally required or medically important vaccines; discuss the relative risks and alternatives with the veterinarian.
Important: An adverse event can be reported by the veterinary team or owner to the manufacturer and the appropriate regulator. Reporting does not prove causation, but it supports safety monitoring.
TRUSTED SOURCES
Sources behind this guide
American Animal Hospital Association (AAHA)2022 canine vaccination guidelines and subsequent updates ↗Feline Veterinary Medical Association (FelineVMA; formerly the American Association of Feline Practitioners)2020 feline vaccination guidelines developed with the American Animal Hospital Association ↗World Small Animal Veterinary Association (WSAVA)2024 global vaccination guidelines ↗American Veterinary Medical Association (AVMA)Pet-owner vaccination and reaction guidance ↗
Source links are provided so readers can review the underlying guidance. Publication dates and recommendations can change; confirm individual plans with the treating veterinary team.