Yeah yeah, I know I just talked about this, but today I want to answer the question I get ALL THE TIME: Do I really have to give vaccines every every 6 months? Yes. Yes you do. If you need more than my assurance, then read on.

When the immune system attacks

That’s exactly how the horse immune system works. My Docs give vaccines, and your horse’s immune system responds great. By that, I mean it makes antibodies to the diseases the vaccines were for. Those antibodies roam around the body 24/7/365 looking for their target (like Eastern Equine Encephalitis, EEE for short). When they find their target, they attack and fight to the death. When something like EEE attacks, it doesn’t attack with two or three little viruses. It attacks with millions of viruses, which means the body needs millions of antibodies. Even more important in a state like Florida with EEE out there all the time, the body needs to have millions more antibodies ready for the next attack.

There’s something I was supposed to be doing…

That last part is where horses have trouble. You see, the immune system needs to remember what viruses it’s supposed to make antibodies to. The equine immune system suffers from short term memory loss. My Docs give a vaccine, those millions of antibodies get made for a while, then the body starts to forget. That time frame is about 6 months. In some horses, it’s as short as 4 months! A bunch of researchers have vaccinated horses, then checked the blood every month for 6 months to see how many antibodies there are floating around. Turns out that number drops in a big way at 2 months, then does a slow decline over the next few months. Here’s a link to one of these papers, in case you need to read it for yourself. The important thing to note in this paper is that these horses were routinely vaccinated every 6 months for YEARS before this study came out. ← And that’s why horses have to get vaccinated all the time, even when they’ve had them for years.

Can’t you do a blood test?

My Docs often get asked, What if we run a blood test to see if there are enough antibodies? You may not realize it, but that’s a super-complicated question. Until recently, it was tough to find a lab that would run these blood tests, called titers. We do now have a lab at Kansas State University where Eastern Encephalitis, West Nile, and Rabies titers can be run. Next tricky part is deciding how many antibodies are enough. No one really knows. There was some work done many, many years ago to look at how much was enough. However, by today’s standards, the answers they got give us an OK answer, but not a very definitive one.

So yes, for some diseases, a titer can be done, but the answer may still be a big question mark.

Is this true for all equine vaccines?

Pretty much, yep. Horses just don’t respond well to vaccines. They do about the best with Rabies, but even then those antibody numbers drop hard and fast at about 14 months. Rhinopneumonitis (also called Herpes, Rhino, or EHV-1) is weird and will get its very own blog, but suffice it to say the vaccine doesn’t work very well, and it follows different rules anyway.

The influenza vaccine has two different versions: an intranasal one and an intramuscular one. The intranasal one is tough to get antibody levels on. Most of the antibodies hang out in the mucosa lining the nose and mouth so a blood test doesn’t work very well. However, in studies it does a great job preventing the flu for at least 6 months (and really more like 12). The intramuscular vaccine makes antibodies, we can measure them, and they seem to help make the flu less icky, but when compared to the intranasal, it’s no contest.  

Strangles also comes in an intranasal and intramuscular variety. This is another tough vaccine to sum up in a sentence. Tell you what, I’ll write a future blog about Strangles too, just for you guys.

So to answer your questions: When it comes to Eastern Encephalitis, West Nile Virus, and Tetanus, your horse definitely needs to be vaccinated every 6 months at a minimum. Rabies needs to happen at least yearly. The intranasal flu can happen every year. Strangles and Rhino are complicated. If you prefer, a blood test can be done for EEE, West Nile, and Rabies, but knowing what the results mean is tough.

Don’t want to worry about any of this? Leave it all to my crack staff of minions. They’ll take excellent care of your horse so you can worry about how that pesky outside rein works.

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