This section provides an introduction to vaccinations, including how they protect your horse against potentially serious diseases and their proven safety. Knowing more about how vaccines work can help you make informed decisions about your horse’s health and wellbeing.

If you have any questions about vaccinations after reading this section, feel free to ask your vet, or visit our Advice section.

Read on to find out more about:

  • What vaccines are
  • How vaccinations work
  • Why vaccinations are important
  • Why booster vaccinations may be required
  • The different types of vaccines
  • Possible side effects from vaccinations.

What is Vaccination?

Vaccination is a way of stimulating a horse’s immune system to protect it against harmful organisms (such as bacteria or viruses) without the horse being exposed to the risk of serious illness or death.

To understand how vaccines work, let’s look briefly at how a horse’s immune system helps protect it from disease.

What is the immune system?

  • Your horse’s immune system is designed to fight infection. There are two basic types of immunity – innate and active.
  • Innate immunity refers to the inbuilt methods of defence that are present from birth. These defences range from the protective barrier provided by the skin, through to microscopic immune cells that attack harmful organisms that manage to enter the body. The problem with innate immunity is that it is not designed to target specific diseases.
  • Active immunity is more specific and develops when your horse comes in contact with harmful bacteria or viruses. Active immunity involves the production of antibodies – special proteins that circulate in the body that detect and destroy invading organisms. Antibodies specifically target one bacteria or virus, which is why they are a very effective type of immunity.
  • Vaccination harnesses the power of active immunity, by stimulating the production of antibodies to protect your horse against a specific disease.

How do vaccines work?

Vaccines work by stimulating active immunity. This causes the immune system to produce antibodies that specifically target a particular disease. Most vaccines contain tiny amounts of dead or damaged bacteria or viruses. Because they are dead or damaged, they can’t actually cause disease but they are still capable of stimulating an immune response.

In the future, if your horse comes in contact with the natural form of the bacteria or virus, the immune system ‘remembers’ the organism and quickly produces antibodies that specifically target the bacteria or virus. These antibodies repel or kill the organism, to prevent infection.

Why are vaccines important?

Horses are at risk of a number of serious infectious diseases, some of which can be fatal. Regular vaccinations can help keep your horse safe, by ensuring they produce enough antibodies to fight off a specific disease, if they are exposed to it.

Vaccination is proven to help protect against many serious equine diseases. There are often no specific cures for these, and treatment can be extremely expensive with no guarantee of success. Some diseases can also quickly spread to other horses or, in the case of the Hendra virus, to humans.

How many vaccinations are needed?

To protect against a particular disease, your horse will generally need more than one dose of a vaccine.

  • A primary course of vaccines are given relatively close together to previously unvaccinated horses.
  • Booster vaccinations are given at longer intervals to previously vaccinated horses to maintain immunity.

Primary course vaccinations

    • For most vaccines, one dose does not provide the necessary degree of immunity. More than one dose of vaccine is needed to stimulate the immune system to produce enough antibodies to protect against the disease.
    • A series of vaccinations is required – usually over a period of weeks – to get antibodies to the required levels. These first vaccinations are called the primary course.

Booster vaccinations

  • Over time, the levels of antibodies begin to fall and immunity starts to wear off. To continue protecting your horse, a booster vaccination is given which ‘tops up’ your horse’s immunity levels.
  • The time taken for antibody levels to fall varies for each vaccine. Your vet can advise when your horse needs booster vaccinations to continue protecting against different diseases.

The different types of vaccines

There are a number of types of vaccines that work in slightly different ways.

There are no live or modified-live vaccines available in Australia for horses.

All horse vaccines in Australia are non-living vaccines – they contain bacteria or viruses that have been killed or significantly weakened, rather than live organisms. This can be either a specific part of the organism, or entire killed organisms.

Non-living vaccines will not cause the disease they are designed to protect against. However, non-living vaccines generally produce immunity that is relatively short-lived. This is why multiple vaccinations are required for the primary course, followed by regular booster vaccinations. Non-living vaccines can be further divided into the following:

Killed vaccines

  • As the name suggests, killed vaccines contain bacteria or viruses that have been killed so that they can’t infect the horse. But even though the germs have been killed, the horse’s immune system still reacts to them and produces antibodies against that disease.
  • Some examples of killed vaccines include:
  • Duvaxyn EHV 1,4 (protection against equine herpesvirus)
  • Equivac EST (protection against Salmonella).

Other types of vaccines

  • Subunit vaccines generally work on the same principle but instead of taking a killed version of the entire bacteria or virus, only a specific portion of the organism is used. This tiny portion (the antigen) is the part of the virus or bacteria that stimulates a response from the immune system. Special technologies can be used to make these vaccines very effective at stimulating antibody production.
  • Some examples of subunit vaccines include:
  • Equivac S (protection against strangles),
  • Equivac HeV (protection against Hendra virus)

Vaccination side effects

Vaccinations are proven to have significant benefits for the health of both humans and horses alike. But vaccinations – just like any medicine – can have side effects. However, any side effects to vaccines are generally mild and short-lived.

Think about when you get a flu or tetanus shot – the site of the injection might be sore for a day or so but any discomfort soon disappears.

Given that the diseases prevented by vaccination can be extremely serious or even fatal, the benefits of protecting your horse greatly outweigh the minimal risks.

Remember: there are no live or modified-live vaccines available for horses in Australia. So there is no risk of your horse developing the disease they are being vaccinated against, nor acting as a ‘carrier’ and spreading infection to other animals as a result of being vaccinated.

It is scientifically proven that vaccinations do not weaken or overload your horse’s immune system. Your horse comes into contact with many more antigens in its daily life than are contained in a vaccine.

If you’re concerned about side effects from a vaccination, please contact your vet.

Possible side effects from vaccinations

Possible side effects from vaccinations can generally be grouped into local symptoms that occur at or near the site of injection, or more generalised side effects that may occur more widely in the horse’s body. Symptoms generally resolve without any need for specific treatment. Possible side effects from vaccinations can include:

Local Symptoms

    • a lump, swelling or soreness at the site of an injection that gradually resolves over several days
    • slight muscle stiffness for a day or so.

Generalised Symptoms

  • temporary elevated temperature
  • temporary lethargy or loss of appetite
  • allergic reactions – these are rare but can occur and may require vet treatment. The most extreme form of reaction is anaphylaxis, which only occurs extremely rarely after vaccination.

How are side effects classified

Vaccine safety is treated very seriously and every suspected vaccine reaction is thoroughly investigated by the Australian Pesticide and Veterinary Medicines Authority (APVMA). Anyone can report a suspected vaccine side effect to either the vaccine’s manufacturer or the APVMA.

Side effects are classified depending on how likely it is that vaccination has caused a particular side effect:

    • probable – there is a reasonable likelihood that the vaccine caused the side effect
    • possible – the vaccination is one of several equally possible explanations for the side effect
    • unlikely – the vaccination is unlikely to have been responsible for the side effect
    • unknown – there is not enough evidence to determine whether a vaccination has caused a side effect.

What vaccinations does my horse need?

The vaccinations your horse should receive vary depending on factors such as age, what he or she is used for, geographic location, contact with other horses, and any travel. As part of a preventative care program, your vet can tailor a vaccination protocol specifically for your horse, and ensure that any follow-up boosters are given at the right time.

Don't Wait to Vaccinate