By Dr. Jess Trimble

It’s become evident to the veterinary community the benefits of vaccines far outweigh the risks when it comes to protecting our dogs and cats from serious illnesses. While vaccines are considered safe, you should nevertheless be aware of potential vaccine reactions and side effects, and be able to identify adverse reactions ASAP! Sometimes, you can observe a side effect immediately following the injection. Other times, it may take days or even weeks later to show up, so please stay vigilant.

Mild Side Effects

While some pets have no noticeable side effects after receiving a vaccine, some or all of the following symptoms below are pretty common. They last no more than a day or two.

• Decreased appetite and activity
• Mild fever
• Lethargy
• Discomfort at the vaccination site

Serious Side Effects

More serious side effects are far less common. These are typically associated with allergic reactions, occur within minutes to hours after vaccination, and can be life-threatening – but they are extremely rare (~0.3%). Please seek out emergency care if you notice any of the following:

• Persistent vomiting or diarrhea
• Severe coughing or difficulty breathing
• Fainting or collapse
• Hives or itchy skin
• Swelling of the face and neck 

Occasionally, a small and firm nodule can develop under the skin at the vaccination site. These nodules typically go away within a couple of weeks. You can help it resolve by massaging the area gently for 10-15 minutes once or twice a day.

Lastly, if your dog or cat has had a prior vaccine reaction, make it a priority to tell your vet before it receives its next vaccine. You can avoid some allergic reactions by being proactive. Some vets like to give a dose of Benadryl – you just need to let your vet know.

Emergency Clinic Information

San Francisco Bay Area New York City