Vaccinations Vaccinations are a necessary part of pet care. But in order to limit any side effects or problems, we always conduct an exam to ensure the animal is in good health and able to respond properly to any vaccines given. It is important that owners understand that there may be a mild reaction to a vaccine, often soreness at the vaccination site, lethargy from 24-48 hours, more sleeping than usual and lack of appetite. Any life-threatening reaction to a vaccine is extremely rare and will often occur within minutes or hours after the vaccine is administered. If the owner is concerned, the pet should remain in the waiting room for 30-60 minutes following the vaccine.