Further information on Vaccination
How does vaccination work?
The immune system is the body’s defence mechanism against disease. The body recognises invading viruses and bacteria as ‘foreign’ and its reaction to these ‘foreign invaders’ is called an immune response. The body produces antibodies which destroy or remove the foreign substances.
The essence of vaccination is that it makes use of the body’s natural systems for fighting disease. This is done by introducing a substance to the body which mimics a disease but does not actually cause the disease. The body prepares its immune response, which then is activated if that disease is detected at some time in the future. The vaccine can be introduced by various methods – commonly either by injection or nasally.
In so many respects, vaccination is the ideal way to combat disease. Immune systems are continuously active in the defence against disease, and vaccination simply exploits this system.
How do diseases spread?
All living organisms share the genetic drive to make sure that their species continues to exist. This applies to viruses and bacteria as much as it applies to humans and animals. Disease-causing organisms therefore have built into their structure the ability to spread from one susceptible organism to another. They can be transferred from host to host by physical contact, contact with body fluids, by the consumption of diseased food, transferred by a ‘third party’ (i.e. mosquitoes, fleas, ticks or midges) or they can be airborne, requiring proximity, but no physical contact to jump from host to host. Some diseases are species specific, while others can infect, or are carried by, a range of species.
Does vaccination have any side effects?
Anybody who has ever been vaccinated knows that it can occasionally make you feel quite feverish and poorly for a short while. Whilst this effect is not pleasant, it is a sign that the vaccine is stimulating the body’s disease defences. The perfect vaccine would not cause those effects, but not all vaccines are perfect, although safety is paramount in the licensing of vaccines. Exceptionally there can very occasionally be more severe side effects but they are so rare that the benefits obtained with vaccination far outweighs the risks. If you are concerned about any possible side effects, discuss this with your vet prior to the vaccine being administered to your puppy.
What are the different types of vaccines?
A vaccine must stimulate an immune reaction in the recipient, similar to the immune reaction that the real disease would produce, but the vaccine must not actually cause the harmful effects of that disease. The manner in which the vaccine component is processed in the laboratory is intended to make it safe but sufficiently similar to the disease so that the body recognises it. There are two broad techniques that are used:
Live – a weak or ‘attenuated’ form of the disease is grown in the lab which, when injected into an animal, does not have the power to cause disease.
Killed – the disease organism is killed and prepared into a vaccine, sufficiently similar to stimulate immunity but clearly incapable of causing disease.
Both techniques have their strengths and weaknesses. There are also new genetically modified vaccines coming onto the market. Such vaccines have the ability to better target the type of immunity required and will provide many new exciting possibilities in disease control.
How frequently should vaccines be used?
Vaccination plays a very important role in the control of infectious diseases. Whilst it is recognised that adverse reactions such as an allergic response or a lack of efficacy may occasionally occur, an analysis of the overall benefits and risks strongly supports the continued use of vaccination.
Vets should make a thorough assessment of the benefits and risks on an individual case basis and discuss them with clients when deciding the timing of vaccination and the use of particular vaccines. Such an assessment will need to be based on the Summary of Product Characteristics (SPC), often referred to as a data sheet in the UK, a publicly available document giving particulars of the data package submitted by the manufacturer and agreed by the licensing authority during the authorisation process (found as Product Information Database at www.vmd.defra.gov.uk). The SPC is unique for every vaccine and will provide precise information on the duration of the immunity that can be achieved when that product is administered. It is this information that the vet will use to decide the frequency of vaccination, along with scientific guidelines that are made available by professional bodies (Vaccine (Guidance at WSAVA website). Recent trends in data mean that many products now indicate a duration of immunity of 3-4 years for canine distemper, parvovirus and adenovirus after completing the primary vaccination schedule and the subsequent booster in minimum age puppies. However, some veterinary surgeons may also take into account the World Small Animal Veterinary Association (WSAVA) Guidelines by, for example, giving a full first annual booster before applying the extended duration of immunity claims, or by delaying the second vaccination until the animal is at least 12 weeks of age in some high risk areas or where levels of maternally derived antibodies are expected to be high. It is important for veterinary surgeons to understand that, when departing from the SPC, they do so under their own responsibility.
Vets should therefore use vaccines in accordance with the authorised stipulations and what they know of the prevailing disease trends in their area. If they deviate from the medicinal data available to them and/or use a vaccine not in accordance with the instructions on the label and the SPCs it must be done with good reason and informed client consent.
Some lobby groups have accused the veterinary profession of over-vaccinating – perhaps using vaccine yearly when there may well be a longer lasting immunity to disease. To challenge this view would involve further testing beyond the scientific evaluations already undertaken by the manufacturer to determine the duration of immunity as specified in the SPC.
What are the benefits of vaccinating dogs?
There is no doubt that the use of vaccination has been of huge benefit to our pets by bringing some very unpleasant diseases under control The use of ‘combination’ or ‘multivalent’ vaccines (where several different vaccines are given together) has transformed the control of many diseases of dogs and cats. Virus diseases such as canine distemper, adenoviruses (viral hepatitis) and canine parvovirus used to be scourges. The development of vaccines and their widespread use has brought the diseases in question under control.
The way in which vaccines have been used in dogs is rather different to the way in which they have been used in farm animals. The difference is that whereas in farm animals the aim is to prevent the spread of disease and to protect the herd, in the dog and cat it is the individual animal that vaccine is being used to protect. However, the uptake of vaccination by responsible dog and cat owners who wish to prevent their pet from catching certain diseases has been so great that it has reduced the amount of such disease seen by vets. It has produced some ‘herd immunity’. Prevention is better than cure, especially with diseases such as distemper and parvovirus where if the animal survives it is often left with permanent damage of some kind.