Vaccines are vital in protecting dogs from various dangerous and potentially deadly diseases. However, like all medical interventions, they can sometimes cause side effects. These are typically mild and rare. If you have any concerns about possible vaccine reactions, your veterinarian will be happy to discuss them. Additionally, always inform your veterinarian if your dog has had a vaccine reaction in the past. Vets agree – in almost all cases, the benefits and need for vaccines outweigh any potential risk.    Mild Reactions: These are the most common side effects and are usually short-lived. They may include swelling and pain at the injection site, mild fever, lethargy, and decreased appetite. Sneezing, coughing, or nasal discharge may also be seen after an intranasal vaccine. These side effects should resolve after 1-2 days.  Allergic Reactions: These are less common but more serious and require veterinary attention. Possible symptoms include vomiting, hives or skin rash, and anaphylactic reaction. If you notice difficulty breathing or facial swelling, seek emergency veterinary care.  Rare Side Effects: Very rarely, vaccines can cause more serious issues, such as immune-mediated reactions and tumors at the injection site.