What to Watch For After Your Dog’s Vaccinations

When to take a reaction to the shot in stride. When to contact the vet.


Tens of millions of pets are vaccinated without any problems every single year. You should never hesitate to have your dog receive the vaccinations recommended by your veterinarian. Inoculations prevent devastating infectious diseases and save dogs’ lives.

But like people, many dogs experience mild side effects. In the vast majority of cases, they subside on their own. In rare cases, though, a dog reacts to a vaccine in a way that requires medical attention. How do you know when it’s nothing to worry about, and when you should seek veterinary help?

Mild side effects

The following reactions are relatively common and usually very short-lived. The first three tend to start within hours of the vaccination and dissipate on their own within 24 to 28 hours.

  • Discomfort and local swelling at the vaccination site.
  • Mild fever.
  • Decreased appetite and activity.

If any of these signs last more than a day or two and are causing your dog significant discomfort, contact your vet to make sure all is okay and to see what can be done to make your pet feel better.

  • Respiratory discomfort.

If a vaccine is given through the nostrils rather than with a needle, a dog might experience a mild respiratory reaction — sneezing, mild coughing, or runny nose. This tends not to occur until 2 to 5 days after the shot is given. Don’t be alarmed. But again, if the symptoms last more than 24 hours, contact your vet.

  • Swelling where the shot was given.

One other common mild reaction to a vaccine is the development of 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 become larger or more painful, speak with your dog’s doctor.

More serious side effects

There are some side effects to vaccinations in dogs that are much less common than mild ones but are potentially life-threatening. (Sometimes they are signs of dangerous allergies.) If any of these signs develop with minutes to hours of your dog’s vaccination, seek veterinary care immediately.

  • Persistent vomiting or diarrhea.
  • Itchy, perhaps bumpy (“hives”).
  • Swelling of the muzzle and around the face, neck, or eyes.
  • Severe coughing or difficulty breathing.
  • Collapse.


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