Frequently Asked Questions About VaccinationsMurray Woodbury DVM, MSc.
Specialized Livestock Health and Production Department of Large Animal Clinical Sciences Western College of Veterinary Medicine University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4
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- Why vaccinate?
- How are vaccines designed to work?
- How are they different from antibiotics?
- By vaccinating are we limiting an animals potential to ward off disease on their own or weakening their natural immune system?
- A common thought is that by NOT giving vaccinations we allow the animal's natural immunity to build up on its own. Can you comment?
- Are general commercial vaccinations as effective as vaccines designed on an individual basis for individual farms (autogenous vaccines)?
- Some vaccine manufacturers recommend booster shots for their vaccines. Is it necessary to give these injections?
- Is it necessary to give a booster within the recommended time interval?
- Can you give a brief overview of the licensing process for drugs in relation to the deer industry? Why isn't there anything designed and licensed specifically for deer?
- Do you have any suggestions for how we, as an industry might encourage companies to license products for deer and list dosages specific to deer?
A deer producer would vaccinate his/her animals for the same reasons that producers of other classes of livestock would vaccinate - to decrease the incidence of specific preventable diseases and economic loss in their herd. Remember the old saying "An ounce of prevention is worth a pound of cure". The difference between vaccinating deer, and vaccinating cattle or sheep is that the currently used vaccines are not labelled for use in cervids and are therefore untested in those species. We have no actual scientific proof that they work, only experience or anecdotal evidence. We use them because we have nothing else and because they are thought to at least cause no harm to the animals.
How are vaccines designed to work?
The actual immune mechanism by which vaccines stimulate immunity in a vaccinated animal depends on many things including the nature of the disease causing organism (bacteria vs virus for instance), the state of the organism in the vaccine (live, weakened, dead), the part of the organism used to make the vaccine (whole, part, recombinant), the vaccine carrier (adjuvants, viruses, chemical vehicles) and how the vaccine is delivered (oral, aerosol, injectable).
Whatever the makeup of the vaccine and the type of response that it stimulates in the animal, all vaccines are designed to protect the vaccinated animal against a real-life challenge from organisms found in nature. Vaccines do not protect an animal against all organisms, only those that are included in the vaccine. When vaccinated the animal is actually given a dose of the disease causing organism, but in a harmless or non disease causing state. Instead of creating disease the vaccine stimulates the animal to produce protective cell types, antibodies, and other immune defences against the organism used in the vaccine. When later confronted by an real-life invasion of the same organisms, the vaccinated animal's immune system "recognizes" the invader and summons specific, already made antibodies and cells to overwhelm the infection.
How are they different from antibiotics?
Vaccines are used to prevent disease and antibiotics are used to treat existing disease. Vaccines usually have little or no effect on the course of disease once an animal has become diseased. Vaccines can provide long lasting protection against disease where antibiotics provide only weak, short term protection. Antibiotics are chemicals which either kill bacteria outright (bactericidal) or prevent their multiplication in the animal (bacteristatic). Conventional antibiotics do not kill viruses, neither do vaccines. Vaccines sometimes actually depend on bacterial or virus growth to stimulate immunity in the vaccinated animal.
By vaccinating are we limiting an animals potential to ward off disease on their own or weakening their natural immune system?
The short answer is "no". By vaccinating we are improving the immune capabilities of an animal by giving specific protection against the organism(s) in the vaccine. The animal will not become immune to organisms not included in the vaccine but this does not reduce the animal's general ability or potential to ward off disease on their own.
An animal's immune system can be weakened by situations of poor nutrition, stress or existing disease. Moreover, immune response to vaccine is significantly less in animals weakened by these factors. In disease outbreaks, vaccine failure is frequently blamed on poor products rather than on the unsuitability of the animals for vaccination in the first place and their resulting poor immune response.
A common thought is that by NOT giving vaccinations we allow the animal's natural immunity to build up on its own. Can you comment?
There is no scientific or other proof that this is true. The only thing that builds an animals "natural" immunity is field exposure to pathogens which are overwhelmed by general defence mechanisms, leaving some residual immunity to that pathogen - a sort of natural vaccination. The only problem with this is that the infection that created the natural immunity may have killed that animal under different circumstances.
Are general commercial vaccinations as effective as vaccines designed on an individual basis for individual farms (autogenous vaccines)?
Yes, but it depends on the nature of the disease organism and our ability to make a universal vaccine from it.
Commercial vaccines use organisms or portions of organisms that generally stimulate protective immunity in most situations. They are most useful when the organisms causing disease are identical from farm to farm or from country to country. For example, a disease called blackleg is reliably prevented in most animals by vaccine made from the causative organism, Clostridium chauvei. Vaccines made from preparations of this organism are almost universal in their protective ability.
Autogenous vaccines are vaccines made to protect against specific organisms in a specific situation. There is nothing universal about their effectiveness and they are designed to protect against particular strains of bacteria in unique environments. For example, necrobacillosis is caused by a combination of organisms, one of which is Fusobactrium. The particular type of Fusobacterium and the combination of it's companion organisms tends to change from farm to farm. For this reason, vaccine which protects against necrobacillosis on one farm is often ineffective against necrobacillosis on another farm.
It is not necessary to make an autogenous vaccine for diseases like blackleg. A universal product works well. Conversely, universal vaccine against necrobacillosis frequently gives poor protection. A custom blend of organisms from that farm must be used to create autogenous vaccine. This is literally vaccine generated from the original disease causing organisms themselves.
Some vaccine manufacturers recommend booster shots for their vaccines. Is it actually necessary to give these boosters?
"When all else fails, follow the directions". Even though we are not using these vaccines in the species for which they are licenced, it makes sense that if we expect to achieve the same results we would follow the directions provided with the product.
Not all vaccines require boosters. Those that do are dependent on an "amnestic" response from the animal's immune system. Having "remembered" the antigen in the vaccine from the first injection, the immune system makes more antibody than would be expected with a single injection. This exaggerated response is the one that raises antibody levels into the protective range for extended periods of time.
Vaccines requiring booster injections are generally those containing killed bacteria (bacterins) or those with relatively poor immune promoting properties (low antigenicity). If the booster injection is not given, the job is only partly done. Antibody levels may never reach protective levels and if they do, these levels may not stay for very long.
Is it necessary to give a booster within the recommended time interval?
The recommended interval is usually about 3 weeks apart. If the booster injection is given after the recommended interval, the booster effect may be lost and the immune response will be much lower than needed to provide effective and lasting immunity. In many cases forgetting the booster injection makes the first injection a waste of time and money. In some high risk situations or with some vaccines having low antigenicity it can be necessary to boost immunity every 6 months or so. To get the best results from your vaccination routines, remember to use and store your vaccines according to the manufacturer's recommendation.
Can you give a brief overview of the licensing process for drugs in relation to the deer industry? Why isn't there anything designed and licensed specifically for deer?
The licensing process for drugs used in deer is the same as the one used to licence or "label" drugs for any other species. Deer and elk have not been discriminated against by this process, they have just been omitted. At the time when Canadian licensing was sought for most of the drugs used in livestock, deer and elk were not being farmed in Canada and the need for licensing was unknown.
The governing body responsible for licensing veterinary dugs in Canada is the federal Bureau of Veterinary Drugs (BVD) in Ottawa. In order to have a species listed on the label of a drug as a species for which the drug is intended, the BVD says that extensive testing must be carried out. Firstly the drug must be shown to be safe for the animals to be treated. The drug must then be shown to be effective in treating the condition for which it is to be marketed. After that, it must be shown to not pose any health hazard to humans eating the food products from treated animals when the drug is used according to label directions. A biologic or preventative drug such as a vaccine has separate but similar requirements. One can see that this is a time consuming and expensive process. Each new species or each new therapy for a species (an "indication") calls for a label change and testing, usually from the beginning.
There isn't anything designed and licensed specifically for deer because of the cost and effort involved in doing so. If a pharmaceutical company cannot return the cost of licensing and the label changes in increased profits, then the benefit/cost rule of business makes the licensing unattractive. The potential market for drugs labelled in Canada for use in cervids is too small to warrant the investment needed.
Do you have any suggestions for how we, as an industry might encourage companies to license products for deer and list dosages specific to deer?
The answer revolves around the central issue of research and which benefiting group should pay for it. The BVD would gladly grant a license for the use of any drug in deer or elk if there were sufficient information to allow them to do that under their rules. In today's atmosphere of "user pays" the two beneficiaries of this research, namely the drug companies and the deer producers must work out some arrangement of shared cost in order to accomplish the licensing goal. Waiting for the drug companies to generate this information themselves will not work. See previous question.
The other way to achieve drug licensing for deer and elk species might be to persuade the BVD to change the testing requirements for including new species on existing labels. Current requirements call for testing from scratch or complete re-licensing. Why is it not possible to extend the existing license to include new but similar species? This approval would be based on less extensive testing than would be required of a brand new drug never previously tested in ruminants. In this modified method of licensing, testing would involve fewer animals and shorter trials than currently required. This would make it less expensive and more attractive to pharmaceutical companies while continuing to insure the health and safety of Canadians and Canadian livestock.