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Dairy Today Healthline

When Vaccines Fail

Aug 01, 2011

The reality is that while vaccines offer significant protection against disease, no vaccine can protect 100% of the animals 100% of the time. Here’s why.

thayerBy Travis Thayer, DVM, AgriLabs Technical Services
Vaccines are an essential tool of any animal health program. Most vaccines on the market today are efficacious and safe and, in the vast majority of cases, they provide excellent protection against disease.
However, in some situations, producers experience situations where animals still get disease in spite of adequate vaccination. It is natural to want to blame the vaccine, especially since, in the vast majority of cases, vaccines work extremely well, setting expectations high for producers and veterinarians. 
The reality is that while vaccines offer significant protection against disease, no vaccine can protect 100% of the animals 100% of the time.
So what could be going on when animals break with respiratory disease in spite of having received an appropriate vaccine regimen? In general, this can be attributed to one of three factors: “broken” management, “broken” animals or “broken” vaccine. If one or more of these failures occur, the herd is likely to experience a higher-than-expected level of disease.
Broken Animals:  This means that, for some reason, despite administration of a quality vaccine product that has been handled properly and given at an appropriate time, the animal does not respond properly to the vaccine, resulting in less-than-optimal protection and higher-than-expected respiratory disease. 
There are many factors that could contribute to decreasing an animal’s ability to respond to vaccines. Some of these include extreme weather, high parasite loads, less-than-optimal nutrition, or animals that are stressed by things such as weaning, shipping, etc. In some cases, animals are already infected with a viral or bacterial pathogen when they receive the vaccine. Vaccines are a great management tool, and certainly help to decrease the risk that an animal will break with respiratory disease. However, even under optimal conditions with healthy cattle, not all animals will be 100% protected, which is why revaccination is often necessary.
Broken Management: Sometimes conditions occur which are beyond our control. However, sometimes the way we manage animals or handle vaccine products “sets up” the vaccination program for failure. 
For example, receiving a load of cattle who have just been shipped for two days in the summer heat, vaccinating right after they get off the truck, and expecting optimal protection is just not realistic. Likewise, weaning, castrating, co-mingling different groups of animals, and vaccinating all at once may not be the best possible program for optimal immunity. Each of these events alone causes significant stress, and taken together, the stresses are additive and can suppress animals’ immune systems, causing some or all of the animals to respond poorly to vaccination. 
Another example of a place where vaccine programs do poorly is failure to follow label instructions for vaccines, especially with respect to mixing, storage and handling. Modified live vaccines (MLV) need to be mixed according to label instructions, protected from light and heat and used as soon as possible after they are mixed. A general guideline that many veterinarians recommend is to use them within an hour after they are mixed. Mix up vaccines “as you go” rather than mixing up vaccine for all the cattle that you are going to vaccinate that day. Bacterial products are particularly sensitive to temperature, and excessive cold or heat will not only reduce their effectiveness but can actually damage them, causing release of endotoxins that can make animals sick by themselves, further depressing their immune systems and making them more likely to break with respiratory disease.
Broken Vaccines: While it is certainly possible to see vaccine failure, due to different strains of organisms than that covered by the vaccine, less-than-optimal efficacy, etc., this in reality does not occur very often. In most cases, animal or management factors or even bad weather are more often the cause for vaccination programs that fail to protect animals as well as we expect them to. 
The best way to ensure that vaccination programs work properly is to review your management and vaccination protocols with your veterinarian on a regular basis, and to call your veterinarian for help if animals break with disease despite an adequate vaccination program.
In addition to your veterinarian, vaccine companies have technical service veterinarians who are happy to help sort out (preferably together with your regular veterinarian) what may be going on when you see higher-than-expected disease in your herd. Your veterinarian or animal health supplier can put you in touch with them to help troubleshoot the problem.
After obtaining a B.S. in Microbiology and a DVM Degree at UC Davis, Dr. Thayer practiced dairy production medicine in California’s Central Valley. He joined AgriLab’s technical services group in June 2005. Contact him at 510-910-3126 or
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