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8/8/2019 Vaccines KK

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Vaccines


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The discipline of immunology has it routes in the

early vaccination trials of Edward Jenner and Louis

Pasteur.

Since those pioneering efforts, vaccines have been

developed for many diseases that were once major

afflictions of mankind. The incidence of diseases such as diphtheria, measles,

mumps, pertussis (whooping cough), rubella (German

measles), poliomyelitis, and tetanus has declined

dramatically as vaccination has become morecommon.


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The road to successful development of a vaccine that

can be approved for human use, manufactured atreasonable cost, and efficiently delivered to at-risk

populations is costly, long, and tedious.

Procedures for manufacture of materials that can betested in humans and the ways they are tested in

clinical trials are regulated closely


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Experience has shown that not every vaccine

candidate that was successful in laboratory andanimal studies prevents disease in humans.

Some potential vaccines cause unacceptable side

effects, and some may even worsen the disease they

were meant to prevent.

Live virus vaccines pose a special threat to thosewith primary or acquired immunodeficiency


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Active and Passive Immunization


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Immunity to infectious microorganisms can be

achieved by active or passive immunization. In

each case, immunity can be acquired either bynatural processes


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Vaccine is a Nonpathogenic immunogen thatinduces immunity against a specific antigen whenadministered to a host system.

The first vaccine was developed by EdwardJenner in 1798 against smallpox.

Criteria for being an effective Vaccine

1. Induce long-standing immunity

2. Induce both responses (humoral and cellmediated)

3. Act at appropriate body site

4. Act against specific antigen

5. Must be less expensive or inexpensive6. Easy to store and administrate

7. Be safe

8. Induce Memory


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ClassificationBased on their mode of production

vaccines are divided into two types

1. Conventional vaccines,

2. Newer vaccines


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Conventional vaccines The vaccines that are prepared by using the whole

organism or sub cellular components using simple

techiniques like heat killing, attenuation etc. arecalled conventional vaccines.

Based on the source agent the conventional

vaccines are further sub divided into

(A) Heterologous vaccines

(B) Homologous vaccines


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Heterologous vaccines The vaccines which were produced from

one organism and used against another

organism are called heterologous vaccines

For example the small pox vaccine

produced by Jenner was by using Vaccinia

viruses.


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Homologous vaccines The vaccines which are produced and used against

the same organism are called homologous

vaccines. For example the vaccine produced from Hepatitis

B virus is useful against hepatitis only. The

homologous vaccines are further classified into

(I) Whole organism vaccines

(II) Sub cellular vaccines


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Whole organism vaccines

The vaccines, that are produced by using the

whole organism are called whole organism

vaccines. Many of the currently using vaccines are whole

organism vaccines.

These may be prepared by killing inactivation or

by making avirulent by attenuation. Based on thisthey are divided into two types

(i) Inactivation, (ii) Attenuation.


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Inactivation

The whole organism is inactivated by subjecting toheat or chemicals or irradiation.

With this treatment the organism cannot replicatein the host.

care should be taken so that the epitopes on theorganism should not be lost.

During heat inactivation there is more chance tolose the epitope, as most of the protein epitopes(which are heat sensitive) can lose their structure.

So heat inactivation is generally unsatisfactory. chemical inactivation formaldehyde or alkylating

agents are useful.

For example the polio vaccine salk, is produced byusing the formaldehyde.


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Characteristics of inactivated

vaccines are

Mostly through humoral immunity response

Require repeated booster doses.

More stable

It can never return back to the virulent form


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Attenuation

The loss of ability of a microorganism to cause

significant disease, retaining the capacity to grow

in the inoculated host is called attenuation

(Avirulation).

To attenuate any microorganism it should be

grown for prolonged periods under abnormal

"conditions. This procedure leads to mutations

The mutants which that are suitable for better

growth -in abnormal culture and less suitable to

grow in natural host are used for vaccination.


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Characteristics of attenuated

vaccines The microorganisms in vaccine have the capacity

for transient growth.

They can produce prolonged exposure to immunesystem resulting in production of memory cells

Generally require a single booster

The vaccine is very less-stable

The attenuated viruses can revert to its naturalinfective form.

This is one of the major disadvantage withattenuated vaccines.


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Sub cellular vaccines

vaccines are made of purifiedmacromolecules rather than entiremicroorganisms

Based on the sub cellular component usedfor vaccination Sub cellular vaccines aredivided into

(i)Toxoid vaccines

(ii)Subunit vaccines

(iii) conjugate vaccines


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Toxoid vaccines The vaccines that are produced against the toxins

of microorganisms are called toxoid vaccines.

In case of disease like tetanus, diphtheria and botulism the toxins of the bacteria is only

responsible agent to cause the disease.

The toxoid vaccines induce the antibodies

production against toxin but no immunity is

induced against the .bacteria.


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Subunit vaccines

The vaccines, which are made with

only a single immunogenic protein from thepathogen of interest.

The vaccine hepatitis B is a subunit Vaccine.


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NEWERVACCINES

The conventional vaccine production approachhas been improved with recombinant DNAtechnology, hybridoma technology and automatedantibody synthesis.

Different types of newer vaccines are:

(A)Recombinant vaccines

(B) DNA vaccines


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Recombinant vaccinesThe technique involves isolation of gene,

insertion of gene into carriers (vectors),

introduction of gene and carrier into a

suitable host.


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DNA

vaccines In this method DNA sequence encoding for an

antigen with suitable promoters can be inserted

into a plasmid. Engineered DNA should be administered

intramuscularly

The DNA then codes for its specific protein. This

results in producing long- lasting humoral and cell

mediate immune response to the DNA coded

protein (antigen).

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