Dr Ali Butt
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Vaccine is a biological
preparation that provides active acquired immunity against a disease in a host.
Vaccines may contain microorganism or virus in live attenuated or killed form
or protein or toxin from an organism.
Vaccination is a simplest, safest and
most effective way of protection against harmful diseases. Vaccines use body’s
natural defense mechanism (antibodies) to produce resistance against the
specific disease. These antibodies remember and destroy live microorganism in
future against which vaccine was used.
The reason to vaccinate animals is to save them from preventable diseases and reduce the risk of illness and death. In some cases, vaccine is done against diseases of zoonotic importance hence to save human population. Vaccine is considered cost effective method to prevent animals from disease instead of treating them.
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Vaccine can be of multiple types based on contents and method of preparation.
1- Live attenuated vaccine in which microorganism is weakened. These vaccines produce strong and long-lasting impact e.g. hepatitis A vaccine etc.
2- Inactivated vaccine uses killed microorganism that cause the disease. These give weak response hence frequent doses are required e.g. measles vaccine etc.
3- Subunit, recombinant, polysaccharide and conjugate vaccines use specific pieces of microorganisms like protein or casing. These vaccines give strong immune response as compared to others e.g. Hepatitis B vaccine etc.
4- Toxoid vaccine uses toxins made by germs and immunity is against those toxins e.g. tetanus vaccine etc.
5- mRNA vaccine in which mRNA gives instructions to cells how to make a protein of the germ in order to trigger an immune response. These vaccines don’t contain live virus so there is no risk of the disease e.g. COVID-19.
6- Viral vector vaccine uses genetic material which gives instructions to cell to make a protein of the germ. Modified version of viruses are used as a vector to deliver protection like influenza virus that are used against COVID-19.
Another way to classify vaccines is water based and oil based. Water based vaccine gives weak immune response with higher amount and more frequent injections of antigens. In contrast oil-based vaccine induce long lasting immune response with small dose of antigens.
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Vaccines are prepared in 5 general steps i.e.
1- Generating the antigen by growing pathogen in culture media.
2- Releasing and isolating the antigen from growth material.
3- Purifying the antigen using various separation techniques.
4- Adding adjuvants and preservatives.
5- Packing.
Sometimes vaccines don’t give required results called vaccine failure.
These are either vaccine related or host related factors that cause vaccine failure.
1- Problems with vaccine potency, stability or storage can reduce effectiveness.
2- Improper storage, transportation and administration can result poor response.
3- Improper attenuation can lead to diseased animal or decreased immunity.
4- Improper dosage can alter the results.
5- Animals with weak immune system may not respond properly.
6- Age and nutrition of vaccinated animal may change the outcome.