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While vaccinations are particularly topical as conversation fodder this year (will you get the Pfizer or the AZ?) they have played an important part in human and animal disease prevention for over 200 years. So let’s talk about the history of vaccines and how they work…

Vaccines through history

Bacteria and viruses have been the scourge of people throughout the ages – bubonic plague, cholera, typhoid, smallpox, measles, polio, flu – the list goes on. Infectious disease also cause significant losses in animals, with rinderpest and foot and mouth disease examples of the worst.

In 1796 (225 years ago), English doctor Edward Jenner noticed that people who had been infected with cow pox did not suffer as much from smallpox. He collected some pus from the lesions on his milk maid’s hands and inoculated his gardener’s son (!!)). Two months later he exposed the boy to smallpox: no disease. This was the start of the journey to eradicate what was a truly horrible disease (as you can see in the photo below). Prevention of animal diseases also caught the attention of scientists, with Louis Pasteur pioneering anthrax, rabies and chicken cholera vaccines in the 1880’s.

Since that time, a multitude of vaccines have been developed for both humans and animals.  Diseases are chosen because:

  1. They cause significant economic loss e.g. tuberculosis and brucellosis in cattle
  2. They are highly infectious e.g measles in people, parvovirus in dogs
  3. There is a high risk of disability or death, even with treatment e.g. polio in people, salmonella in calves
  4. Once infected, death is inevitable e.g. rabies in people and clostridial diseases in animals (examples include tetanus and botulism)

How do vaccines work?

Vaccines stimulate the body’s immune system to make antibodies against a specific virus or bacteria. They do it by exposing the immune system to the pathogen in a way that won’t cause disease. Vaccines may be composed of:

  • Killed virus or bacteria
  • Live virus or bacteria that have been treated so that they don’t cause disease
  • Parts of the virus or bacteria

mRNA vaccines are a new type of vaccine that instruct the body to MAKE the part of the virus or bacteria that stimulates antibody production.

Vaccines also contain substances that alter how often they need to be given, and how they can be given (such as under the skin, in the muscle or up the nose). Generally vaccines need an initial course of two injections: the first teaches the body to recognise the disease, the second stimulates it to make large numbers of antibodies (as shown in the diagram below). Vaccines are usually formulated to stimulate a response against multiple diseases.

(Note, colostral vaccines have a particular aim: cows are immunised against diseases so that their colostrum has higher levels of antibodies for their calves)

What is herd immunity?

Prior to Covid-19, the term “herd immunity” rarely made the news! Herd immunity is generally considered the result of vaccinating a population to improve overall blood antibody levels (rather than relying on a natural infection, which risks disease, death, and economic losses along the way). Herd immunity is particularly important when a disease has a severe impact on a part of the population that is unable to be vaccinated – babies and whooping cough is a good example.

Vaccines don’t eliminate disease entirely. They do, however, reduce the severity of clinical signs and the numbers of bacteria or virus particles that are shed.

There are many examples of what happens when vaccinations lapse and herd immunity wanes, such as outbreaks of feline parvovirus in feral cats in Melbourne and measles in Samoa.

What diseases can we vaccinate our dairy herds against?

There are some diseases that every farm should vaccinate against, in order to protect against diseases that can have significant economic impact if they occur:

  • Clostridial diseases (examples include black leg in cattle and enterotoxemia in sheep and goats)
  • Leptospirosis (can cause abortion and sick calves, vaccination also prevents people from getting infected)
  • Pestivirus (vaccination of heifers prior to their first joining is a good safeguard against economic losses, particularly if joined to sexed semen)
  • Vibriosis (a cause of infertility, vaccination of bulls helps prevent poor reproductive performance)

There are other vaccines that are done on a farm-by-farm basis, depending on the disease status or risk of disease:

  • Salmonella is present on some farms and can be a significant cause of disease, death and antibiotic resistance
  • Botulism is not common, but if it occurs the impact is most severe in herds that feed mixed rations
  • Pestivirus vaccination may also be needed in milking herds naive to the disease
  • Silirum vaccination of calves reduces the clinical signs and shedding of Johne’s Disease in adult cattle

Vaccinating tips

Vaccines can be expensive and take time and effort to administer. As antibodies are proteins, animals must be in good general health for their immune system to respond effectively to vaccinations and produce the antibodies needed to fight disease.

  • Vaccines must be kept cold and stored in a fridge when not in use. Some vaccines also have a short shelf life after being opened
  • Use eskies and cold packs to keep vaccines cool while out in the field
  • Vaccinating in extreme heat is not recommended: during summer try to vaccinate animals early in the day when it is cooler
  • It is important that no more than 2 vaccine products are given on one day and different injection sites are used (remember some vaccines contain 7 or 8 components)
  • Some vaccines are given in the muscle, others under the skin. It is important to read the label for the appropriate dose and route of injection
  • The injection sites must be clean and dry; change needles regularly
  • Vaccinations can be timed to coincide with routine events such as weighing or Teatsealing