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"Doc, you sold me the vaccine and my cow still got sick!"

Livestock Update, October 1999

John F. Currin, DVM, Extension Veterinarian, Production Management Medicine,
R. Tom Bass, DVM, Production Management Medicine,
Tom Bailey, DVM, MS, Extension Veterinarian, Production Management Medicine,
Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech

Reasons for Vaccination Failures
One of the most difficult things to understand is how a cow can develop a disease she has been vaccinated for. While no vaccines work 100% of the time, some vaccines prevent disease better than others. Many factors can affect how vaccines will work. The following is a list of some of the most common reasons vaccinations fail to provide protective immunity.

1. Improper Vaccine Handling -- Vaccines need to be properly handled prior to use to ensure that they are still effective when injected. All vaccines require refrigeration and modified live vaccines are very susceptible to ultraviolet light (sunlight). Vaccines that require mixing are only good for a few hours after mixing so care should be taken to only mix them as needed.

2. Failure to Follow Label Directions -- The most common mistake is giving the wrong dose. Take time to read the label each time before you work cattle. Another common mistake is to use the liquid part of a vaccine without first mixing it with the powder.

3. Improper Injection Technique -- Proper injection technique is essential to ensure that the vaccine get in the cow. Giving a "hair injection" is a common mistake. These happen when the needle never enters the skin or enters and passes back out through the skin before injecting. When using a pistol-grip syringe care must be taken to ensure that no air bubble is present inside the syringe. If an air bubble is present not enough vaccine will be injected when the trigger is pulled. Pistol-grip syringes also need to be checked periodically to ensure that the correct dose is actually being administered.

4. The Existence of Multiple Subtypes of a Bacteria or Virus -- Some viruses and bacteria have multiple subtypes (strains). Some vaccines only protect against a specific subtype. However, many vaccines will either contain antigens of multiple subtypes or cross-protect against them. Pinkeye is a disease that can be caused by multiple subtypes of the bacteria Moraxella bovis. There are more than 20 subtypes of this species of bacteria. Several pinkeye vaccines contain multiple subtypes but none of them protects against all of the subtypes. When the subtype of Moraxella present on your farm is also present in the pinkeye vaccine you are using, then the vaccine is effective. If your subtype of Moraxella is not present in the vaccine it will not work as well, if at all.

5. Vaccination at the Wrong Time -- Ideally, cattle should be vaccinated 3-4 weeks before they are likely to be exposed to or develop a disease. This will ensure there is sufficient time for the animal to develop protective immunity

6. Exposure to High Levels of Disease -- If an animal is exposed to enough bacteria or viruses its immune system can be overwhelmed and the animal will develop the disease. Calf scours is a good example of this scenario. If calves are born in a dirty, cold, and wet environment no vaccination program will protect against the level of exposure to the disease-causing organisms.

7. Poor Immune Response -- Cattle that are highly stressed or sick at the time of vaccination will have a decreased immune response. Cattle receiving inadequate nutrition may also respond poorly to vaccination. This includes cattle in poor body condition (thin cattle) and those consuming rations deficient in certain nutrients such as selenium, vitamin E, copper, and zinc.

8. "Las Vegas Syndrome" -- No vaccines work 100% of the time, so some animals will develop disease even if they have been properly vaccinated for that disease. There is nothing wrong with these calves they are just unlucky.

9. Interference of Passive Immunity -- Calves that are vaccinated during the first 2 months of life may not develop a proper immune response because of interference with the immunity they received from suckling the cow's colostrum. Vaccines given to calves during the first 2 months of life may have to be boostered in order for the proper immune response to develop.

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