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Vaccination, also known as immunization, is the administration of antigenic material a vaccine to stimulate an individuals immune system to develop adaptive immunity to a pathogen and has been found as the most effective way of preventing infectious diseases. Vaccination is largely responsible for the eradication of infectious disease such as Small pox and restriction of diseases such as Polio, measles, whooping cough, tetanus and many others.
In Vaccination, the antigenic material that is used is a non-pathogenic form of a microbe or its products, such as toxins, so that on encounter with the pathogen an immune response is generated. The active antigen of the vaccine may be intact but inactivated, or attenuated forms of the microorganism, or purified form of the pathogen that are highly immunogenic. Several vaccines which are currently in use these days include hepatitis, polio, measles, whooping cough, chicken pox and many others.
An ideal vaccine has got highly immunogenic antigens that can elicit a strong appropriate response for the particular antigen, should not cause side effects or infection after administration; a single dose of it should be adequate for a life-time immunity and can be given orally, should be easy to produce and inexpensive. However there are few vaccines that fall under all of these attributes.
There are vaccines that are administered by hypodermic injection since most are not easily absorbed by the intestines. Those that are easily absorbed by the intestines are given orally. Also the route of administration can be determined by the type of response that should be produced by that particular vaccine. Injections normally produce a systemic immune response and oral or the respiratory route primarily produces a mucosal immune response with a predominance of the immunoglobulin A.
When the antigen has been introduced, the body recognize as foreign. B cells
Vaccines that have been made so far which are available for clinical use fall under these categories;
Inactivated vaccine- which consists of bacteria or viruses that are cultured then killed by heat or formaldehyde so that they will not replicate. The antigenic component remains intact enough to evoke an immune response. Booster shots can be required by this type of vaccine to reinforce the immune system since the bacteria or virus does not reproduce. Examples include
Hepatitis A, polio, rabies, yellow fever
Safe and more stable than the live vaccine
Produce a weaker immune response than the live vaccine
It is easy to store and transport since it does not require refridgeration
Usually require additional doses or booster shots to evoke a stronger immune response
Attenuated vaccine- this is when live virus or bacteria with low virulence are administered which replicates slowly. The antigen continue to be present in the system therefore the need for boosters is less often. Examples include Small pox, measles, polio, typhoid
1. produce a strong immune response which often last for a lifetime with one or two doses
1. There are possibilities that the antigen can mutate back to its virulent form
2. cheaper to prepare
2. It is not easy to transport to remote ares since it must be refridgerated to stay potent
3. Easy to prepare for viruses than bacteria which is complex in its antigenic structure
3. can cause infection in people who are immune compromised like HIV patients
Subunit vaccine- Only the antigenic part of the pathogen is administered without introducing the whole microorganism. There is isolation of a specific part of the pathogen or toxins(in some bacteria) that is administered by itself. Examples of vaccines include Hepatitis B,
Target a very specific part of the microbe and therefore it is able to mount a specific immune response
Identifying the best antigens is difficult and time consuming
Fewer antigens are used therefore there are lower chances of adverse effects
Toxoid vaccines- These are microbial toxins that are treated with formalin to render them non pathogenic.Examples of vaccines that employ the technique are Diptheria and Tetanus vaccines
Useful in complex bacteria that secrete toxins
The immune response produced can fail to eliminate the microorganism giving it chance to mutate and produce other virulent factors
Immune system produces antibodies to the toxin which is a virulent factor
Conjugate vaccine- These arevaccines that are made by conjugating polysaccharides that are secreted by bacteria with proteins that can be easily recognized by the immune system.Examples of vaccines include the H. influenzae vaccine.
Immune response is mounted against polysaccharide coated bacteria hence no risk of the microbe mutating back to virulent form
The immune response mounted is not as strong as live attenuated vaccines
Allow infant immune system to recognize certain bacteria
DNA vaccines- These are genes for epitopes that are administered into the body. The body cells then make antigen molecules and display them on their surface. These antigens then mount an immune response resulting in the body producing antibodies against the antigen.
No risk of developing diseases since no microbe is administered
Still in experimental stages
Produces a strong immune response
Recombinant vector vaccines- These are genes that code for virulent epitopes of the pathogen that are inserted into a genome of harmless virus or bacteria. When administered, the epitopes of the pathogenic or virulent antigens mount an immune response.
Elicit a strong immune response since they resemble the virus that causes diseases
Still in experimental stages