Vaccines. You hear from us every spring and autumn about getting your seasonal vaccines, but why do equids seem to need vaccines so much more often than your other animals?
First, a quick explainer on vaccine vocabulary. Any vocabulary in quotes is taken from the World Health Organization (WHO). While they are talking about people, and therefore the quotes will use “people,” the terminology is the same across species, which means for humans, horses, donkeys, dogs, and degu, the vocabulary is the same, so feel free to substitute "donkey" or "mule".
Efficacy: “efficacy is a measure of how much the vaccine lowered the risk of getting sick”
“If a vaccine has 80% efficacy, it does not mean that it will only work 80% of the time. It means that in the vaccinated population, 80% fewer people will contract the disease when they come in contact with the virus”
Effectiveness: “Vaccine effectiveness is a measure of how well vaccines work in the real world.” This takes into account those who could not be admitted to the drug trials, such as the sick, elderly, very young, etc.
Timing and Doses: “Vaccines offer strong protection, but that protection takes time to build. People must take all the required doses of a vaccine to build full immunity. For two-dose vaccines, vaccines only give partial protection after the first dose, and the second dose increases that protection. It takes time before protection reaches its maximum level a few weeks after the second dose.” When you get a new animal with an unknown vaccine history, your vet may suggest initial dosing protocols instead of just boosters, administering multiple doses of any vaccines that require it. Don’t forget, most vaccines take about two weeks after their final dose or booster to reach full protection.
Titers: Serum titers are blood tests that measure whether or not an individual is immune to a given disease(s). More specifically a quantitative serum titer is a titer with a numerical value indicating their actual degree of immunity to a disease(s). If the titer for a specific disease shows that they're not immune, they need to get vaccinated or re-vaccinated (also known as getting a booster).
If your animal has a particularly adverse reaction to a particular vaccine, or if you are concerned about over vaccination, you may want to discuss a titer test with your vet. In some cases you may be able to order a titer to decide if your animal requires a booster or not.
Duration of Protection/Effectiveness: The amount of time a vaccine is considered effective. The amount of time before a vaccine requires a booster.
Back to the question above: why do donkeys and mules generally get vaccines twice a year, when most other species get them only once a year, or even less? Well, that depends on many factors.
Some vaccines, such as West Nile virus (WNV), are highly effective, but the duration of protection and effectiveness is quite short, typically only around six months or less. After this, the effectiveness will wane drastically. This is why your vet will typically recommend a WNV vaccine every spring, prior to mosquito season beginning. However, depending on the duration and severity of your mosquito season, your vet may also recommend this vaccine be boosted in the fall. September and October typically see the highest numbers of WNV in the United States, as vaccinated equids lose their immune response, but mosquito numbers stay high.
Other viruses requiring vaccines, such as various influenza, are constantly mutating. Each year the vaccine your animal receives may have different strains than the previous years. This is the same reason you get a flu shot every year; the efficiency didn’t necessarily wane, but the virus mutated to something your antibodies will no longer recognize.
Still other vaccines, such as rabies, may be effective for more than a year, but the studies simply haven’t been done to establish the duration of effectiveness. Titers can help decide if your animal needs this vaccine or not. However, titers cost money to run, and they require multiple vet visits should they determine your animal needs a booster. Vet visits cost money. Because of this most people simply choose to go ahead and vaccinate yearly, without checking the titers. Since rabies is a public health threat, and 100% fatal to all species who are able to contract it, humans included, protection through vaccination is essential. Most people choose the cost effective and easy solution of yearly vaccinations over titers as this vaccine is highly effective and well tolerated.
Why can’t we just assume rabies vaccines last three years, like it does in dogs?
Even when discussing the same virus, different species’ immune systems react differently to vaccines. Take tetanus, for instance: in humans doctors recommend a tetanus booster every seven years. In sheep, however, veterinarians recommend a tetanus vaccine every year. Furthermore, in goats it's recommended they receive a tetanus booster every six months, as the efficiency simply wanes very rapidly in goats. It’s for this reason we can’t generalize vaccine efficiency from species to species, and why we can’t assume that a rabies vaccine will remain effective in equids for the same duration as it does in dogs or cats.
Who can help decipher which vaccines you should give your animals? Your vet is your biggest ally in the fight against viruses.
When you make a vaccine appointment, be sure to tell your vet what sort of activities you like to do with your animals, with whom you like to do them, and where you plan to take your animals in the next year. If you board your animals, please let your vet know all the same information about the other equids in the facility. This will help your vet decide which vaccines are appropriate for your animal.
Core vaccines are those considered necessary and appropriate for the majority of cases, and include Rabies, Tetanus, and mosquito borne viruses (WNV, EEE, WEE). Additional risk based vaccines are used on a regional and case-by-case basis depending on the activities you choose to do with your animals and what diseases are seen in your region. For instance, in Arizona we don’t typically vaccinate for botulism, but one of the sources of botulism in equids is round hay bales (moisture gets into the bale, and botulism starts cookin’). If you plan to take your donkey up north for the summer, and feed them in a pasture with round hay bales, your vet may recommend a botulism vaccine. Another example is anthrax. Anthrax isn’t found in Arizona, but it is endemic to the Texas panhandle. If you are taking your donkey to Lubbock, you may want an anthrax vaccine. Similarly, if you don’t travel anywhere, but the horse in the pen next to you is trying to qualify for the Junior National Finals Rodeo, hitting up three barrel races a weekend? You might want to consider influenza, herpes, and strangles (Strep. Equi subspecies equi) vaccines.
When you call your vet to schedule health certificates for travel don’t forget to tell them where you are going, what route you intend to take, and what sorts of activities you plan to do. This way they can let you know if your donkey needs any additional vaccines.
Finally, don't forget to inform your vet if your animal has ever had an adverse reaction to one or multiple vaccines in the past. Post-vaccine malaise is fairly common as your animal's immune system activates a response to the vaccines, and your vet may want to administer an anti-inflammatory, such as Banamine, if your long ears tend to have a stronger reaction. Because of this, even if you typically don't notice a substantial reaction in your animals, it's often kindest to not plan to work, haul, or exhibit them for 2-4 days after they receive their vaccines. This allows them to feel a little bit down in the comfort of their own pen, without anything being expected of them.
Thank you to Dr. Minuto of Chaparral Veterinary Medical Center for the collaboration on the above information.
