Modern vaccines are extremely effective and safe. However, it is common for many pets to experience mild side effects following vaccination, similar to those that humans experience. Rarely does a pet need veterinary medical attention for these normal, minor side effects.

What are some common side effects of vaccination?

Some of the most common mild side effects that can be seen after immunization include:

  • Redness, mild swelling, and tenderness at the vaccination site
  • Decreased activity levels (fatigue)
  • Loss of appetite
  • Low-grade fever
  • Nasal discharge, sneezing, coughing, or other respiratory symptoms, which may occur up to 2 to 4 days after an intranasal vaccine (vaccination with drops or sprays via the nostrils) is administered

If any of these signs lasts more than 24 hours or if your pet appears extremely uncomfortable, notify your veterinarian.

It is also common for a pet to develop a small, firm nodule at the vaccination site.

It should begin to shrink and vanish within 14 days. If the swelling lasts longer than 3 weeks or appears to get larger or more painful, contact your  veterinarian.

Are there other possible side effects of vaccination that I should watch for in my pet?

Other less common but more serious side effects can occur within minutes to hours after vaccination. These reactions are considered to be medical emergencies, and you should seek veterinary care immediately if any of the following occur:

  • Collapse or fainting
  • Difficulty breathing
  • Persistent and severe coughing
  • Small, red, raised, itchy bumps over the body (hives)
  • Swollen or puffy eyes, muzzle, or face
  • Persistent vomiting or diarrhea

Before immunization, tell your veterinarian if your pet has had any previous vaccine reactions, regardless of how insignificant they may seem. These patients will benefit from a pre-vaccination treatment with an antihistamine or considering splitting up multiple vaccines with adequate time between them as recommended by your veterinarian. If you have any concerns that your pet may have a serious vaccine reaction, wait at your veterinary clinic for 30 to 60 minutes after vaccination.

The vast majority of the millions of pets vaccinated each year experience no problems. Closely monitor your pet, and report any problems to your veterinarian as soon as possible. Vaccines save countless lives and prevent devastating infectious diseases from threatening our pet loved ones. If you have any questions or concerns, please discuss them with your veterinarian.