Vaccination Is Also Called Immunisation Biology Essay


Vaccination is also called immunisation where the immune system is stimulated by a non-pathogenic form of microbe, killed or weakened, or its product usually a toxin or one of its surface proteins so that on encounter with the pathogen, a protective response is generated which is characterised by the production of circulating neutralizing antibodies and memory cells to mount a secondary immune response which is more rapid than a primary immune response. Vaccines can either be prophylactic or therapeutic and can be administered either by injection to generate systemic immune response or orally/respiratory/eye dropped to stimulate primarily mucosal immune response with IgA predominating. However a vaccine does not guarantee full protection from the disease due to a number of factors that affect its effectiveness. The characteristics of an ideal vaccine can be summarised as safe and effective. These characteristics include:

Cheap , thermostable and easy to produce

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Administered orally with minimal side effects

Single dose should give life-long immunity

Can appropriate immune response for the targeted antigen

Do not cause infections in host that is non-pathogenic

There are many types of vaccines, basically seven types, and these include live/attenuated , inactivated/killed, toxoid, subunit, conjugate, DNA(naked DNA) and recombinant vaccines. All of them have their advantages and disadvantages


These are live bacteria or viruses that have been weakened to reduce their virulence by cultivating them in conditions that disable their virulent properties, so that they cannot cause infections in healthy people. They multiply in the human host and possible continuous antigenic stimulation over a long period of time. This includes vaccines for small pox, varicella, measles, typhoid, rabies, yellow fever, mumps, BCG and polio.


Stimulate both humoral and cellular immune system and therefore offer long-term immunity with one or two doses

Since they are administered by the natural route of infection, they can induce secretory i.e. IgA and systemic immunity

Because the virus is alive and can spread from individual to individual, that can give rise to herd immunity

Immune response is raised to all protective antigens

Cheap to prepare and easy to administer


Poor stability and must be refrigerated to stay potent and thus may be difficult to transport to countries where there may be no refrigeration systems

Potential to revert and mutate to virulence

Possibility of under attenuation

Contraindicated in immunosuppressed patients

Potential for contamination in cultured cells

Heat labile

Increased risk of allergic reactions due to large amounts of antigen involved

Difficult to create especially for bacteria because bacteria have thousands of genes that makes it harder to control


The natural whole pathogenic microorganism (virus or bacteria) is produced in quantity and inactivated or killed by chemical, antibiotics, radioactivity, heat or physical procedure that eliminate infectivity without destroying the antigenicity of the pathogen e.g. bubonic plague, Japanese encephalitis, cholera, Influenza, Hepatitis A, Polio, Rabies and Pertusis.


Safer i.e. unable to cause infections and more stable since no live vaccine is used

Does not require refrigeration and thus easy to store and transport as freeze dried forms

Can be used in immunocompromised individuals

Excellent stimulant of passive antibodies in colostrum


Since the cells are never infected with the virus, they do not elicit full cellular immune response/ long term immunity because Tc cell response recognise endogenously synthesized viral antigens in association with MHC I molecules on surface of infected cells.

Need for an adjuvant to activate antigen presenting cells by keeping antigens at injection site

Local reaction is common

Short lasting immunity and onset of immunity is slow

Need several doses and it activates weaker immune system response

Inactivation, such as by formaldehyde in the case of the Salk vaccine, may alter antigenicity

Some vaccines do not raise immunity - failure of the vaccine is common

In polio there has been shortage of monkeys and in small pox there have been failure in inactivation leading to immunization with virulent strains

C) SUBUNIT VACCINES (non-recombinant)

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This encompasses use of a peptide site encompassing the major antigenic sites of the pathogen antigen. Protein subunit or epitopes of the pathogen, rather than introducing an inactivated or attenuated microorganism to an immune system (which would constitute a 'whole-agent' vaccine), a fragment of it can create an immune response. Thus subunit vaccines can contain anywhere from 1-20 or more antigens. Increasing purification may lead to loss of immunogenicity and this may necessitate use of an adjuvant. This includes Pneumococcus, meningococcus, Japanese encephalitis, Haemophillus influenza, tick-borne encephalitis, Hepatitis B e.t.c.


Is specific - Targeted to very specific parts of the microbe

Few antigen so low chances of adverse reactions


Identifying the best antigens is difficult and time consuming

Increased purification may lead to loss of immunogenicity thus need for use of an adjuvant

Poor antigenicity


It is useful in bacteria that secrete toxins or harmful chemicals. This vaccine is useful when a bacterial toxin is the main cause of illness. Toxins are inactivated by treating them with formalin to form detoxified toxins called toxoid, which are safer to use as vaccines. When the immune system receives a toxoid vaccine, it produces antibodies to the respective toxin, which will neutralize the toxin when encountered e.g. tetanus, diphtheria toxoid vaccines or Crotalus atrox toxoid vaccine for rattle snake bite.


Efficacy very high

Safe because they cannot cause disease and cannot revert to virulence

Cannot spread to unimmunised individuals

Stable (thermostable, humidity stable) , and long-lasting

Less risk of contamination

Excellent stimulant of passive antibodies in colostrum


Need for an adjuvant

Local reaction common because of an adjuvant and because the production of excess antibodies can activate classic complement pathway resulting in tissue damage

Onset of immunity is slow


Certain bacteria have polysaccharide outer coats that are poorly immunogenic. Polysaccharide coatings make it difficult for a baby or young child's immature immune system to see and respond to the bacterium inside. Polysaccharide vaccines are poorly immunogenic in children under 2 years old and do not stimulate long term immunological memory. By linking the outer coat polysaccharides to proteins, the immunogenicity of the polysaccharide is increased as illustrated below e.g. Haemophilus influenza type B vaccine, Pneumococcus vaccine. Thus conjugation is the process of attaching (linking) the polysaccharide antigen to a protein carrier (e.g. diphtheria or tetanus) that the infant's immune system already recognises in order to provoke an immune response


Allows infant immune system to recognise certain bacteria

Safe for immunocompromised people

Lower chances of adverse reactions


Requires booster shots, expensive

Time consuming


Genes encoding major viral antigen (that is a target for neutralising antibody) is inserted/cloned into another non virulent viral vector so that the cloned gene is expressed and the protein produced during viral replication


Both humoral and secretory immunity are stimulated

Plasmids are easily manufactured in large amounts

DNA is very stable and also thermostable thus transportation easy

A DNA sequence can be changed easily in the laboratory i.e. respond to changes in the infectious agent can be monitored

Mixture of plasmids could be used that encode many protein fragments from viruses so that b road spectrum vaccine could be used

The plasmid does not replicate and encodes only the proteins of interest

There is no protein component and so there will be no immune response against the vector itself

Because of the way the antigen is presented, there is a cell-mediated response that may be directed against any antigen in the pathogen. This also offers protection against diseases caused by certain obligate intracellular pathogens (e.g. Mycobacterium tuberculosis)


Potential integration of plasmid into host genome leading to insertional mutagenesis


DNA encoding specific viral protein injected into the host, taken up by cells, transcribed into mRNA, translated into viral protein and the protein expressed on the surface of the host cells either alone or in association with MHC molecules and will be recognised as foreign by the immune system.

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Since no infectious agent is used, it is safe

Expression is long term, the gene may integrate into cell DNA and be stably expressed so that long term immunity may be solicited

Since the antigen is endogenously synthesized inside cells, it elicits a strong cellular immune response

Once a gene is cloned, DNA is inexpensive to make and is stable so the vaccines are inexpensive

No adjuvant is required


It is still in experimental stages - limited information about the efficacy in humans

Potential integration of plasmid into host genome leading to insertional mutagenesis

Induction of autoimmune responses (e.g. pathogenic anti-DNA antibodies)

Induction of immunologic tolerance (e.g. where the expression of the antigen in the host may lead to specific non-responsiveness to that antigen)


Health Protection Agency. The different types of vaccines used and their composition. Immunisation Department, Centre of Infections: Core topic 4