Vaccination has been called “medicine’s greatest triumph,” responsible for nearly eradicating childhood killers such as polio and smallpox. Vaccinating your horse protects him against equally frightening diseases, including tetanus and sleeping sickness, both of which are almost always fatal. In the past decade, however, vaccine opponents have raised concerns about vaccinations and even begun to question whether they’re necessary at all.

Should you continue to vaccinate your horse? If so, which vaccines should you give? It’s hard to know what’s right.

In this article, I’m going to investigate the top five arguments I’ve heard made against vaccination in both human and veterinary medicine. While some of the concerns are legitimate, many more are not?

Once you’ve heard all sides, I’ll give you a set of rational questions to ask to make educated decisions about your own horse’s vaccination plan.

The Arguments
Point #1: Vaccines are dangerous. Overheard: “They lead to a hyperstimulated immune system and all kinds of health problems. I’ve read on the Internet that vac- cination causes headshaking and allergies in horses, too.”

Counterpoint: When it comes to horses, there are no legitimate studies that link vaccination to diseases related to an over-stimulated immune system such as allergies or skin disease. The stories you hear are just that’stories. While there may be other reasons to question whether or not to administer a certain vaccine to your horse, this simply isn’t one of them.

Point #2: The side effects are awful. Overheard: “OK, so maybe there’s no scientific proof that vaccina- tion causes other diseases, but the side effects from vaccines are horrible. Every time my horse gets vaccinated he can’t lift up his head for days. Death is even possible.”

Counterpoint: Yes, vaccinations can cause side effects?some more than others. And this is clearly a legitimate reason to consider your horse’s vaccination program carefully. Some horses are more sensitive to vaccines than others, and if yours is one that seems to have a problem every time he’s vaccinated, you may choose to take the minimal-vaccination route. In this situation, the concept of “herd immunity” comes into play: If 80 percent of the population in a herd is vaccinated, the remaining 20 percent have some protection against a serious outbreak.

If your horse is a reactor, you should look at individual vaccines carefully. Vaccines for some diseases are more problematic than others, and different forms of vaccines for the same diseases have different reactivity. Ask your vet to help you decide which vaccines are most important due to exposure risk and severity of disease.

Once you’ve decided which diseases are most important to target, look at the different forms of each vaccine available. For example, killed-virus vaccines may not be quite as effective as modified-live-virus vaccines, yet they typically cause much less significant reactions. And intranasal vaccines for respiratory diseases are often much less reactive than their intramuscular counterparts.

If you’re considering strangles vaccination (a vaccine with high risk for side effects), you can measure antibody levels in the blood prior to vaccinating; if antibody levels are high, your horse is at greater risk for serious side effects (and could be protected anyway), so don’t vaccinate.

Finally, if your horse is exceptionally sensitive, ask your vet whether it would be advisable to administer a dose of a non-steroidal anti-inflammatory medication such as flunixin meglumine (Banamine?) prior to vaccination to minimize side effects.

As an example, we have a horse in our practice that’s highly reactive to vaccines. He spikes a fever, his legs swell, and he can even act a little colicky afterwards. He lives in a big, busy competition barn, where his exposure risk is high. His vaccination program consists of tetanus?because it’s such a safe vaccine against an extremely dangerous disease?and influenza given intranasally, where side effects are extremely rare. He’s lucky to live in a barn where the other horses are on a solid vaccination program so herd immunity is high. And he receives a dose of Banamine prior to every tetanus vaccine to minimize his risk of side effects.

Point #3: Vaccines are unnecessary. Overheard: “I’ve never known a horse to get any of the diseases we vaccinate against.”

Counterpoint: Guess what? I have. And if you’ve ever seen a horse with tetanus, I can promise you won’t ever want to see it again.

One of the factors contributing to the current trend against vaccination is a bit ironic. We live in the vaccination age. Many of us have never seen these diseases?because they’ve been held in check so effectively by vaccination. Young mothers have never seen a child with polio or experienced a measles outbreak, and horse owners have been saved from the heart- ache of watching their horse die of tetanus following a simple wound. Yet if you look around, there are countless examples where serious outbreaks have occurred that could’ve been pre- vented by vaccination.

Most recently, Eastern equine encephalitis, a form of sleeping sickness, has been on the rise in the United States. Outcbreaks have been reported during the past two years in many states, including Florida, Michigan, New York, Maine, Georgia, Louisiana, Connecticut, New Hampshire, and Massachusetts. This mosquito-borne disease is almost always fatal, can spread to humans, and is completely preventable by vaccination. According to the Center for Disease Control, nine human deaths from EEE have been reported during the past six years. Most of the reported equine cases in recent out- breaks have been in unvaccinated horses.

In 2007, Australia experienced a devastating influenza out- break. Large numbers of horses became ill or died, and the entire equine industry was shut down for many months. Why was this outbreak so severe? Australia had previously been influenza-free?with the result that horses had no natural immunity and were unvaccinated when they became exposed. Had they been vaccinated, this outbreak would’ve been much more easily controlled, and many lives would’ve been spared.

West Nile virus is another interesting case. When this disease first hit the East Coast in 1999, many horses became ill or died. By 2001, a vaccine was developed, and widespread vaccination of horses across the country occurred. As the disease spread west, the incidence and severity declined significantly. The reason? Vaccination clearly played a role. As horses were vaccinated, they became less likely to contract the disease, both limiting its spread and helping to minimize the severity of disease for horses that did become ill.

On the human side, measles and whooping cough, two diseases that were unheard of several decades ago, are on the rise. In fact, a number of reported epidemics have included infant deaths?most commonly in areas where parents are turning away from vaccination.

The lesson here is that we can’t become complacent. Just because we don’t see the diseases at the barn next door doesn’t mean they no longer exist.

Point #4: Vaccines are expensive. Overheard: “You can save hundreds of dollars if you just skip them.”

Counterpoint: This is faulty logic. The cost of vaccination pales in comparison to the cost of treating a serious disease. For example, an annual tetanus vaccine costs between $10 and $15 (it might even have sleeping sickness included in that price). To provide supportive care for a horse affected with tetanus would run in the thousands. And what if your horse doesn’t make it?

Costs associated with less deadly diseases add up, too. Consider an outbreak of a simple respiratory virus in a barn. Although it may not be terribly expensive to treat each individual horse, it can mean weeks or even months of lost training time and missed competitions.

Point #5: Vaccines don’t work. Overheard: “I’ve heard of vaccinated horses still getting the disease in question, so vaccinations aren’t really effective.”

Counterpoint: Simply not true. Although vaccinations won’t completely prevent every instance of disease, they do make a difference. Some, like tetanus and sleeping sickness, are extremely effective for preventing clinical illness. Less effective vaccines can still help keep symptoms to a minimum if your horse does get sick. And most play a big role in pre- venting outbreaks by helping to control spread. In fact, estimates from human medicine say that we’ve added 30 years to our average lifespan just because of vaccination.

So while you can’t expect vaccination to be 100-percent protective, you should recognize the importance of a vaccination program for keeping your horse healthy.

Decision-Making
So, should you vaccinate your horse with every vaccine avail- able, or not at all? Just as with most great debates, the answer to the vaccine question rests somewhere in the middle. Most

importantly, you should evaluate risk vs. benefit to your horse for every individual vaccine. In other words, is the risk of the vaccine greater than the risk of the disease? If so, just say no. If not, consider vaccination.

When deciding whether or not to vaccinate, it’s especially important that you get your information from a reliable source. Your veterinarian is likely to know more about the different vaccines available than anyone?and is certainly more reliable than the Internet or your barn buddies. If you’re a scientific type and need to see solid proof of efficacy or safety studies, your vet can provide you with those answers in addition to his or her personal opinion.

To help you decide on a rational vaccination program for your own horse, ask the following questions about each vaccine you are considering:

How bad is the disease? Is it almost always fatal, or likely to spread to humans, such a tetanus or EEE? If so, vaccinate if you can. For diseases that are usually mild or easily treatable, such as strangles, vaccination may not be as important.

What is your horse’s exposure risk? Does your horse live in a pasture by himself with no exposure to other horses? If so, rabies vaccination might be more important than influenza due to his potential exposure to wild animals that carry the rabies virus. Does he live in a stall in a busy competition barn? He’s less likely to contract rabies, but vaccinating against influenza would be advised.

Where you live and your horse’s lifestyle play big roles in determining his risk for specific diseases. Ask your veterinarian for advice.

How effective is the vaccine? There’s no doubt about it: Some vaccines are more effective than others. And a vaccine that’s more effective is more worth giving. Vaccines for tetanus, Eastern/Western encephalitis, and rabies are all known to be highly effective (and with minimal side effects?see be- low). In most situations, it just makes sense to vaccinate.

On the opposite end of the spectrum is equine herpes virus (rhinopneumonitis). Although the vaccine for this disease may help minimize signs, it’s unlikely to prevent illness completely, and has no efficacy at all against the most severe, neurologic form of the disease. It may not make sense to administer this vaccine unless exposure risk is very high.

What type of side effects can you expect? Some vaccines carry much greater risk of side effects than others. If a vaccine is known to cause more reactions, and/or if your individual horse seems particularly sensitive to it, that could be one to skip?particularly if the disease is a less serious one and/or your horse’s risk of exposure is low.

The take-home message? Vaccination is truly one of medicine’s greatest triumphs. Take advantage of it. By asking the right questions, you can protect your horse against devastating disease with minimal risk through a carefully designed vaccination plan.