Vaccines stimulate the immune system of the animal to produce antibodies.  Antibodies (or immunoglobulins) are proteins created by cells in the blood. Antibodies can also be created in various lymphoid tissues that can be found in the intestine or upper respiratory tract. These specific proteins help to destroy various infectious organisms that can cause disease. Cattle also produce antibodies when they are naturally exposed to infectious organisms. Vaccines are certainly a primary component of our modern herd health programs, but it is important to remember that they rarely provide absolute protection and other management components such as biosecurity, nutrition and environmental management also play important roles in protecting the herd from infectious diseases.

On this page

• Key Points
• Immunology 101: Definitions
• The Immune System
• Types of Vaccines
  • Modified Live Vaccines
  • Killed Vaccines
• Vaccination Cost-Benefit Calculators
• Routes of Administration
  • Injectable Vaccines
  • Intranasal Vaccines
• Why Don't Vaccines Always Provide Protection?
• Some Important Points to Remember When Using Vaccines
• Modified Live Vaccines in Breeding Animals and Pregnant Cows
• Vaccine Reactions
• Vaccination Protocols

Key Points Vaccines train the animal’s immune system to recognize disease-causing viruses, bacteria, and parasites (infectious pathogens) so that it can respond quickly when the animal is exposed to the real thing. Vaccines need to be given prior to disease exposure so that the immune system has time to develop these protective mechanisms. Vaccines should be distinguished from other therapeutic drugs such as antimicrobials.  Vaccines are primarily used to prevent a specific disease from occurring by creating immunity. Antimicrobials and most other therapeutic drugs are used to treat or control a specific disease condition using chemical means rather than through the animal’s immune system. Vaccines can be divided into categories based on whether they are killed or modified live and by their route of administration (injectable vs intranasal). The immune system is extremely complex, but there are two basic components called humoral immunity (concerning antibodies) and cellular mediated immunity (which is associated with other cellular protection mechanisms). Vaccines can stimulate both types of immunity. Vaccines are a key component of our herd health programs but rarely provide perfect protection. Their efficacy can be diminished due to inadequate nutrition, poor biosecurity, and poor environmental management. Read the label on any vaccine you are about to use in your cattle. The dose, withdrawal times, expiration date, timing, route of administration and safety information are all there. This is important for all vaccines but especially so for some modified live vaccines that can cause abortion if administered inappropriately. Work with your veterinarian to design a vaccination protocol that is appropriate for your herd.  Issues such as exposure to other herds and geographic differences in disease risk will make every herd somewhat unique. Vaccines that protect against infectious bovine rhinotracheitis, bovine viral diarrhea, and clostridial diseases should definitely be a part of every herds’ vaccination protocol. However, the timing of administration and the other vaccines that need to be used will be highly dependent on each herd’s management and disease risks.

 

Immunology 101: Definitions

Antigen: Any substance capable of inducing an immune response such as viruses, bacteria, toxins, and parasites.

Antibody (Immunoglobulin): A protein that is produced as the result of the introduction of an antigen into an animal. Antibodies are created within certain blood cells and in lymphoid tissue associated with the upper respiratory tract and intestinal tract. Antibodies react specifically with a particular antigen or one closely associated with it.

Passive immunity: Antibodies that are passed on from the cow to the calf through colostrum. These antibodies provide immune protection to the calf until it is able to create its own antibodies.

Active immunity: When an animal actively produces its own antibodies as a result of being exposed to an antigen. This can occur with a natural infection or when we vaccinate animals.

Mucosal immunity: Immunity associated with mucosal lymphoid tissue sites such as the intestinal tract, tonsils and upper respiratory tract. Antibodies are created that are present on mucosal surfaces which may help to neutralize a pathogen before it gains a foothold. Intranasal vaccines may be better at creating mucosal immunity.

Systemic immunity: Most injectable vaccines focus on creating systemic immunity where antibodies are created in the blood and extracellular fluid. Once a pathogen gains entry to the blood stream, the antibodies can potentially neutralize it.

Pathogen: Disease-causing agent such as a bacteria, virus or parasite.

Naïve animal: An animal that has never been exposed (through natural infection or vaccination) to a certain bacteria or virus before and therefore has no immunity to it.

The Immune System

When cattle are exposed to infectious pathogens, the immune system is stimulated to respond to these infections. It takes time for this complex machinery to respond to a pathogen when it is initially exposed to the antigen (either through vaccination or natural infection). As a result, antibodies aren’t created in time to prevent disease from occurring on initial exposure. However, the immune system is able to “learn” and develop a specific response to a pathogen (a disease-causing agent) such as a particular bacteria or virus or parasite. This is important because when an animal is exposed to the disease for a second time, the immune system has memory cells that are programmed to respond to antigens they have previously encountered. The immune system can now respond much more quickly in creating antibodies as it already has the needed components to create the necessary antibodies. This allows the body to “throw off” the infection, often without any signs at all.

Vaccines work by using an altered antigen that does not cause disease, but rather essentially causes the immune system to think it has been invaded by the actual infectious bacteria or virus. The immune system then creates antibodies along with memory cells that may remain for months into the future. If the animal becomes exposed to an infectious disease pathogen, its immune system can respond rapidly and prevent an infection from occurring.

Two Major Components of the Immune System

Humoral Immunity

Humoral immunity is that part of the immune system that results in the production of antibodies.         

• An antibody is a small “Y” shaped protein produced by immune cells in the blood or on mucosal surfaces. They are also known as immunoglobulins.
• The shape of the end of the “Y” allows the antibodies to interact with specific proteins and sugars and to bind to them. It is a bit like a lock and a key mechanism.
• You need a specific antibody to bind with a specific protein on a bacteria or virus or parasite.
• When an antibody is recognized as being useful for fighting infection, the body immediately up-regulates production of that particular antibody type.
• Antibodies are made by B lymphocytes, a type of white blood cell (WBC).
• Each B lymphocyte produces a different antibody shape.

How Do Antibodies Work?

• Antibodies bind to the attachment proteins (antigens) on bacteria or viruses and prevent them from attaching to body cells (e.g. E. coli calf scours vaccines – the E. coli causing calf scours binds to the wall of the gut using an antigen protein called K99). Antibodies to this K99 antigen protein prevent the E. coli from attaching and it is swept through the gut and is unable to colonize or cause disease.
• When antibodies bind to a foreign antigen, they can signal the start of other cellular defenses targeting it directly to the invader, destroying bacteria.
• Bound antibodies can also help target the cells of the immune system to phagocytose (eat) the invader.
• Many bacteria produce disease by releasing protein toxins. Antibodies can bind and inactivate these toxins preventing disease (e.g. 8-way vaccine contains eight inactivated clostridial toxins).

Cellular Immunity

Humoral immunity and antibodies are just one aspect of the immune system that protects against disease. Cell mediated immunity involves the activation of specific white blood cells that are able to actually destroy certain body cells where viruses or bacteria may be hiding. Cell mediated immunity can also stimulate cells in the immune system to release proteins called cytokines that can signal other cells to initiate an inflammatory response. This may be even more important than antibodies against certain bacteria and viruses that tend to hide in the host body cells. Cell mediated immunity is much more complex and difficult to understand, however, it does not involve antibody production. Vaccines can help to stimulate cell mediated immunity as well as humoral immunity.

Types of Vaccines

Vaccines can be divided into two main categories, modified live vaccines and killed vaccines.

Modified Live Vaccines (MLV)

These vaccines contain living bacterial or viral organisms. The infectious organism has been “modified” by growing the virus in abnormal host cells or by growing a bacteria on an abnormal media. As they replicate this cycle over and over, the virus or bacteria begins to lose some of the factors that may cause disease and the newly modified living bacteria or virus can now stimulate immunity without causing disease. These vaccines often are produced with two separate vials, a sterile solution or diluent and a powder that are mixed together just before using. A newer modification of the MLV are genetically engineered vaccines where the pathogen is genetically altered usually through a mutation or gene alteration. Most MLV are only available through veterinarians to ensure that producers receive appropriate instruction on their use.

Advantages of Modified Live Vaccines:

• Only need a small dose as the living organism actually replicates inside the animal
• May not require a second (booster) vaccination
• Can create a slightly more rapid immune response
• Vaccination with MLV tends to create a stronger and longer lived immune response
• Tend to have a shorter meat withdrawal time
• Tend to do a better job of stimulating cell mediated immunity as well

Disadvantages of Modified Live Vaccines:

• Require very careful storage to avoid killing the live organism (refrigeration)
• Require on-farm mixing
• Require careful handling and clean syringes to avoid killing the live organism
• Must be used immediately after mixing and cannot keep a partially used vial
• Can cause abortions if given to naïve pregnant animals

Killed Vaccines

Killed vaccines usually involve isolating a field strain of a bacteria or a virus from an outbreak of disease, growing the pathogen, then killing it through chemical or physical means (e.g. adding a chemical such as formalin or by using ultraviolet light). This killed organism can then be injected without causing disease, but the various proteins on the bacteria or virus that cause an immune response are still present. A variation of the killed vaccines are toxoid vaccines. Some bacteria such as the clostridial organisms that cause blackleg, tetanus, redwater and other diseases do most of their damage by releasing toxins. These toxins can be produced in a laboratory and then inactivated through chemical means.  Clostridial vaccines (7- or 8-way vaccines) that are commonly used in the cattle industry are the main example of a toxoid vaccine.

Advantages of Killed Vaccines and Toxoids:

• No possibility of vaccine organism spreading between animals
• Safe for pregnant animals – minimal risk of abortion
• No on-farm mixing required
• Can store (refrigerated) and re-use partially used vials if sterile techniques are used

Disadvantages of Killed Vaccines:

• Need a lot more antigen as the organism cannot replicate within the host
• Usually need two doses to get an adequate immune response because the vaccine antigen does not multiply within the vaccinated animal as it can with MLV
• Cell mediated immunity is not usually stimulated quite as efficiently

Vaccination Cost-Benefit Calculators

The BCRC has two calculators that help beef producers determine potential savings from vaccinating cattle.

The Bovine Respiratory Disease (BRD) Cost-Benefit Calculator allows producers to input the number of feeder calves, price, feed weight, cost of gain, days on feed and expected fed cattle price to see the potential savings from sourcing feeder cattle that have been vaccinated for BRD.

Click to download [.xlsx file | 95kb]

With the Bovine Viral Diarrhea (BVD) Cost-Benefit Calculator, producers input herd size, expected price, animal weights, cost of vaccine and labour to estimate the potential savings from vaccinating cattle for BVD.

Click to download [.xlsx file | 96kb] Updated Nov. 2021

Routes of Administration

Just as vaccines can be divided into categories based on whether they are modified live or killed vaccines they can also be divided into categories based on their route of administration.

Injectable Vaccines

Traditionally most of our vaccines were originally administered by injection either subcutaneously (under the skin) or intramuscularly. These types of vaccines tend to be best at stimulating systemic immunity although they may create some level of mucosal immunity as well.

Intranasal Vaccines

These vaccines are more geared towards stimulating mucosal immunity although some systemic immunity may also be created. These vaccines interact with the lymphoid tissue in the upper respiratory tract to create antibodies at the surface which can then potentially inactivate the pathogen before it enters the animal. Although we don’t have many oral vaccines in the cattle industry, these would also fall into this category as they tend to stimulate local mucosal immunity in the gut.

See the BCRC blog post, Intranasal Vaccines Are Timely And Effective, for more information on the use of these types of vaccines.

The following webinar provides an overview of how to use nasal vaccines effectively.

Why Don’t Vaccines Always Provide Protection?

Pink eye vaccination research conducted at VIDO

Veterinarians are often asked to investigate apparent vaccine failures in which vaccinated animals do not seem to be adequately protected by the vaccine which was given. Although very few vaccines can guarantee 100% protection, many cases of vaccine failure are caused by one of the following reasons:

1. The animal was already incubating disease when the vaccine was administered. The lag time for the immune system to start producing antibodies is one to two weeks following vaccine administration. If the animal is exposed to the virus or bacteria prior to the vaccine being administered or even shortly afterwards the vaccine may appear to be ineffective. However, it is simply because the animal was already incubating disease before the immune system could respond to the vaccine.

2. The vaccine was administered incorrectly. Read the label and follow the directions! Consult your veterinarian if you have questions. Many vaccines can be given subcutaneously (under the skin) but some can only be given intramuscularly. Some vaccines are only designed for intranasal application. Incorrect administration or less than adequate dosages may not stimulate an adequate immune response. Check your automatic syringes to ensure that they are working correctly and administering the correct dose of vaccine.

3. The vaccine was not boostered correctly. As stated above, it is very important to follow the label directions on all vaccines. Many killed or inactivated vaccines and some modified live vaccines require a booster vaccine to be given at some point after the initial vaccination. The initial response to one of these vaccines is often somewhat short-lived and is not especially strong. After the second or booster vaccination, a much stronger immune response is seen which is of much longer duration primarily because the immune system’s memory cells can now respond much more quickly. This is known as the secondary or anamnestic response.

4. The timing of the vaccine was incorrect. With many vaccines it is important to match the animal’s immune response to the time period of highest risk for disease. Vaccines do not provide immediate protection to the animal. They typically require several weeks to develop peak levels of antibodies after a vaccine is given. This may be shortened if an animal has previously been vaccinated as their immune system will have a secondary or anamnestic response which is faster than the initial immune response. 

Most cases of respiratory disease in weaned beef calves happen during the high-risk period after weaning and transportation to the feedlot with disease often seen shortly after arrival to the feedlot. Calves that are vaccinated prior to this risk period and have had adequate time for immunity to develop will usually have better immunity during the high-risk period than calves that are vaccinated when they arrive in the feedlot.

Acknowledgements

Thanks to Dr. John Campbell, Professor and Researcher in the Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, for contributing his time and expertise in the development of this page.