Nothing is perfect – including our immune systems – and vaccines are not without their risks, although they are exceptionally rare.
- Allergic Reactions: These are rare in pets – less than 1% of vaccinated pets – but just like a pet can have an allergy to pollens or dust mites, they can also have an allergy to a protein in a vaccine. If your pet has a vaccine allergy, you will see the reaction within a few hours of vaccination, with symptoms ranging from vomiting, hives to a puffy red face. When these occur, they can be addressed by treating the allergic reaction and your veterinarian documenting the reaction. Pets that have an allergic reaction can sometimes have reactions prevented with anti-histamines around the time of vaccination, but this may become a reason for your veterinarian to not to use a particular vaccine for your pet.
- Auto-immune diseases: Pets with auto-immune diseases have abnormal immune systems that have a hard time differentiating normal cells in the body from foreign invaders. These are rare, and vaccines don’t cause auto-immune disease, but pets with auto-immune diseases typically aren’t recommended to have vaccines administered out of caution that stimulating the immune system might also trigger their auto-immune condition.
- Injection site sarcomas in cats: Extremely rarely – around 1 in 10,000 – cats have been found to develop a type of cancer called a sarcoma where an injection was given. Being so rare, they are still not well understood – there are reports of them developing at any injection site – but they are thought to be more attributable to adjuvanted, killed-virus vaccine injections, such as the Rabies and Feline Leukemia Virus vaccines. They are hard to study due to their extreme rarity, but this is why vaccines in cats are administered over the tail or far down on a limb, for extra precaution.
So when are vaccines not recommended?
- Medically ill patients: Those fighting off severe illness may not be recommended to receive vaccines until their illness has been resolved. There are exceptions to this, but an individual whose immune system is already engaged may not mount as effective of a response to a vaccine.
- Pets with compromised immune systems: Pets on chemotherapy, radiation therapy, on immune-suppressing steroids or suffering from other condition(s) that interfere with normal immune system function may not be recommended to receive vaccines. Not only are they unlikely to mount a sufficient immune response to the vaccine – and therefore be less likely to benefit – they may also be at risk of becoming ill if given a modified live vaccine.
- During Pregnancy: Certain vaccines are not recommended to be given during pregnancy so as not to risk the developing kittens or puppies.
- Pets with a history of adverse reactions: If a pet is one of the unlucky few who has a history of auto-immune disease or unmanageable allergy to a vaccine, they will typically not be recommended to challenge that known risk.
Although vaccines are not without their risks, these risks are rare. The benefits of vaccines – preventing severe, untreatable or even deadly diseases – is great. For the gross majority of pets, this means the benefits far outweigh the risks of vaccines, which is why we use them!