Let me start by saying that I don’t know much about human vaccines. What I do “know” is that, with very limited exceptions, kids have to have them before they start school. They are meant to protect kids from serious/dangerous (sometimes even deadly) diseases, diseases that can become epidemics if kids are not vaccinated. Now a day’s kids get all the vaccines all rolled into one…at least I think this is correct.
You may not know this, but twice a year (spring and fall), many domesticated horses are vaccinated. These vaccines are designed to protect them from serious/dangerous (sometimes even deadly) diseases (Eastern and Western encephalomyelitis, West Nile virus, tetanus, and rabies, as well as region-specific vaccines such as Potomac horse fever, botulism, and Venezuelan equine encephalitis). Also they may be vaccinated for diseases that can become epidemics (strangles and equine influenza) if the horses are not vaccinated. Oh yes, and the vaccines are all rolled into one.
This practice of routinely vaccinating and using combined vaccines (3-in-1 or “3 way” or sometimes even 5-in-1 or “5 way”) is usually not an issue, though you may be advised to give your horse a day off after getting shots.
However, this may be standard way of doing things may not be best for all horses. Case in point: The first time my Andalusian Gelding, Kody, got his Spring shots, things did not go well. As I recall he got a “3 way” plus a rabies shot. I was working when I got a call from the barn manager who was assisting the vet with all the horses getting shots that day. Kody is a good boy and stood quietly for his shots (unlike my mare who always gives the vet grief) but he was having a very bad reaction. He was lethargic, running a fever and in general not doing well. The barn manager advised me that she had called the vet when she discovered the problem and he had asked that she just keep an eye on Kody, “let me know if things get worse.” The good news is that Kody did recover pretty quickly, though he passed (in his manure) 5 very large “stones”. This was actually a very good thing, as the stones could have caused him to colic (gut impaction) but what it tells me is that the vaccines caused him to have a very serious intestinal issue due to his vaccines.
Kody fully recovered. He never gets all his shots at one time and every year I talk to the vet about what he really needs. Would I ever not give him shots? Probably not, as the risk of serious disease is always an issue. But, I am much more thoughtful about his vet care, and especially about why, when and how he gets his shots.