HOW DO VACCINES WORK?

As farmers, we often have to give our cattle vaccines to prevent diseases.  Often, farmers ask what vaccines to use for what disease, but it is very important to know and understand how vaccines work and what their functions are.

What is a vaccine? what is the purpose? how do vaccines work?

A suspension containing live, modified or killed micro-organisms or toxins.  This suspension, when administered stimulates the animal’s immune system to produce antibodies/antigens which help fight the disease, should the disease occur.  For example, we are often told to vaccinate our herds against anthrax annually.  What the vaccines do, they contain anthrax causing organisms in the ‘harmless’ form that the body can fight against.  And in the process, when there is an outbreak of the disease, the body already recognizes the disease and has developed antibodies already to fight off the disease.

Boosters and immunity time frame

Vaccines give different lengths of immunity. Some vaccines such as the Brucella S19 which fights against the Brucella virus in heifers is only given once because it has a long term immunity response.  Most vaccines are reapplied every year as the immunity only last for a year.  This is what is called boosting (boosting animal’s immune system) i.e Supavax for anthrax, Blackleg/black quarter and botulism. The function of the booster is to optimize the effectiveness of the vaccine, by maximizing the possibly of the fight against disease. 

Colostrum is the thick milk that comes during the first few days after a cow has given birth.  This milk is very important, and it is always required that the cow should suckle.  Colostrum contain antibodies that the mother has produced, and this gets transferred to the calf and help with disease fighting.  As part of your management plan, insure that calves suckle colostrum. The process is passive immunity.

Why vaccines fail?

Sometimes vaccines fail.  There are several reasons why vaccines fail.

Improper administration

Dosage - wrong dosage may result in vaccination failure.  Always use the recommended dosage when vaccination cattle.  Some vaccines, the dosage is expressed in ml/kg of animal weight.  If the recommended dosage is 1ml/10kg of an animal, than the dose is 30ml for a weight of 300kg.  Using less will result in vaccination failure.

Area of vaccination – There are 3 main areas of vaccination.  Mainly, subcutaneous (SQ on some labels) is when you vaccination through the skin, between skin and flesh. The intravenous injections are giving through the vein (usually by very experience people/VET), and finally, intramuscular (IM) injection which is given through the muscle.

Needle hygiene – Using dirty needles will result in vaccination failure.   Always sterilize needles and syringe by boiling in water (for at least 15 minutes). 

Improper mixing of vaccines

Different pH and dilutents – could completely alter the chemical composition of the vaccine. 

Improper timing

Too early – if vaccines are given too early in calves, they will interfere with antibodies that were passed on from the mother to the calf via the colostrum. So follow directions on the vaccination label on what age to vaccine.

Too late - the disease is already in process.  Other vaccines such as antibiotics must be given.  Give the vaccines that help fight the disease, not the once that prevent the disease.

Animal factors

Environmental stress – animals that are stressed have weak immune systems.  As a result, vaccines that prevent diseases are not effective. Stress such as little grazing (in overstocked farms), long distance travel to drink water, climate change (no rain) all effect animals.

Transport - cattle movements from area to area is very stressful for animals.  If vaccinated, this could result in vaccination failure.

Weaning stress - Never vaccinate with weaning. This reduces the effectiveness of vaccine.  Vaccinate either before or after weaning.

Storage – improper storage, especially for live vaccines can destroy active ingredients, causing vaccination failure.  Store vaccines as instructed, keep away from direct sunlight, keep the temperature as recommended.

Use after expiration – will reduce effectiveness of vaccine.

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