Hi Karen,
So I’m going to start off with by talking about what vaccines actually do. They’re essentially a way of tricking the body into thinking that it is suffering from an infection, so that it can then eliminate a true infection at the very early stages when it’s just starting before it can start to affect the rest of the body. A vaccine does this by the administration of either a dead virus, bacteria or a live version that has actually been modified so that it can’t fully replicate, or it can’t cause the full-blown disease that an unmodified bacteria or virus would do.
As a result, we’ll often actually see mild side effects, which are just signs that the body is essentially fighting a mild infection. I know personally that after I have a tetanus vaccine, my arm really aches for a couple of days and I feel pretty rough for the next 24 – 48 hours and that’s pretty similar to what we can expect with our pets in some cases. So fever, lethargy, inappetence, weakness, stiffness or even tenderness and sometimes local swelling at the area of an injection and vaccination really is not all that uncommon and that can absolutely manifest as shaking or trembling in some dogs. These side effects are more common in younger animals in my experience, and most dogs actually don’t get any kind of problem or they’ll just be a little bit quiet.
If a dog or cat experiences these side effects, they typically resolve after about 24 to 48 hours. They don’t need any specific treatment, just a bit of TLC at home and they’re soon right as rain. We’ve got to remember they’re protected from a potentially fatal disease. That’s not to say that side effects or serious side effects are completely non-existent. The risks are very rare but more serious side effects can be an anaphylactic reaction resulting in breathing difficulties, collapse and ultimately death. We can get vomiting and diarrhea, we can get generalized swelling of the face and neck and we can also get something called injection site sarcomas, typically in cats. They are very rare, but they are tumors that develop at the site of repeated injections so they’re not necessarily vaccine related. I think it was first thought that they were vaccine-related, but they are injection site sarcomas. So it can be injections for other reasons and they cause these really nasty aggressive tumors. So those are the serious side effects, but we don’t want to overstress those because they are very uncommon.
For more mild side effects, a vet might give some anti-inflammatory medication at the time of vaccine if you know that your pet has had one of these side effects in the past. Obviously, if they’ve had a more serious vaccine reaction, if they’d been very unwell, if they’ve had a suspect anaphylactic reaction, if they’re vomiting, have diarrhea, if they’ve kind of collapsed, then we really need to be careful with giving follow-up vaccines. So there are different types of vaccination but we also need to weigh up the benefits against the risks to an individual. So if it’s felt that there are going to be serious health risks as a result of vaccination then we need to question if it’s really essential in that individual.
I hope this helps.
Dr. Alex Avery
