Vaccination

Vaccination is a process involving introducing deactivated/ weakened

disease-causing microbes into a person, or a vaccine is administered to
a person to generate immunity from that disease. Vaccination is
generally injected or administered orally. It is the drug (weak
pathogen/ inactivated) that is administered to a person to prevent the
onset of a disease.

What is an Immunization?
It is the ability of the human body to produce an immune response
either naturally, or through vaccines. These approaches develop
immunity or resistance to a specific illness. Immunization can be
defined as the process by which a person is made to fight against a
particular disease by the administration of a vaccine.

Difference Between Vaccination And Immunization

Vaccination Immunization
The process involves using vaccines to trigger an The process of making one resistant to
immune response to protect against an infectious disease usually through
infections/diseases. vaccination.
It is usually injected or administered orally It is not administered in any way. The
body develops resistance from
vaccines.
Imovax Rabies is the trade name for rabies vaccine The body builds up immunity through
this vaccine for the disease rabies.
Vaccination does not guarantee complete resistance Complete immunity occurs when the
to a disease person fully recovers from the disease.
Usually, if mutation happens to microbes, it might Similarly, variations of a disease impact
render the vaccine ineffective (this is the reason why the body’s ability to generate an
common cold has no vaccine) immune response.

Definition and History of Vaccines

According to the CDC, a vaccine is a preparation used to stimulate the body’s immune
response against diseases. Vaccines are usually administered through needle injections, but
some can be administered by mouth or sprayed into the nose.
Types:
Whole-Organism Vaccines (First Generation Vaccine)
 Many vaccines that were developed early consist of an entire pathogen that is either killed
(inactivated) or weakened (attenuated) so that they cannot cause disease. They are known as
the whole-organism vaccines. These vaccines elicit strong protective immune responses.
1. Inactivated (Killed) Vaccine
 These were produced by killing the pathogen (bacteria, virus, or other pathogens) with
chemicals or heat, or radiation.
 The killed pathogen cannot cause disease, and this means that they do not replicate in the
host’s body.
 Advantage: These vaccines are stable and safer than the live attenuated vaccines
 Disadvantage: The major disadvantage of this type of vaccine is that it elicits a weaker
immune response and therefore, it requires more vaccine dosages and a booster dose as well,
so as to confer protective immunity.
 Examples of Inactivated Vaccines include poliomyelitis (sulk vaccine), rabies, typhoid,
cholera, pertussis, pneumococcal, rabies, hepatitis B, and influenza vaccines.
2. Live-attenuated vaccines
 These vaccines are prepared from a whole organism, by weakening their pathogenicity so that
they cannot cause disease but can induce an immune response, hence the term attenuation.
 These vaccines elicit strong immune responses because they are similar to the actual disease
pathogen and hence they confer a life-long immunity after only one or two doses, therefore
they are very effective.
 Disadvantages: There is a remote chance that the weakened germ can mutate or revert back to
its full strength and cause disease.
 Live attenuated vaccines should not be given to individuals with weakened or damaged
immune systems.
 To maintain potency, live attenuated vaccines require refrigeration and protection from light.
 Examples include Measles/Mumps/Rubella (MMR) and Influenza Vaccine Live, Intranasal
(FluMist®), Polio (Sabin vaccine), Rotavirus, Tuberculosis, Varicella, Yellow fever.
Subunit Vaccines ( 2nd Generation Vaccine)
 These are vaccines that are prepared by using components or antigens of the pathogen. These
components can stimulate the immune system to elicit appropriate immune responses.
 They are also known as acellular vaccines because they do not contain a whole cell, but just
part of a cell of the bacteria or virus.
1. Polysaccharide Vaccine
 Some microbes contain a polysaccharide (sugar) capsule which they use for protection and
evading the human immune defenses, especially in infants and young children.
 Therefore, these are vaccines that are prepared using the sugar molecules, and
polysaccharides from the outer layer of a bacteria or virus.
 They create a response against the molecules in the pathogen’s capsule. Normally these
molecules are small hence they are not immunogenic (can not induce an immune response on
their own). Hence, they tend to be ineffective in infants and young children between 18-24
months, and they induce a short-term immunity associated with slow immune responses, and
slow activation, and it does not increase antibody levels and it does not create an immune
memory.
 Therefore, these sugar molecules are chemically linked to carrier proteins and work similarly
to conjugate vaccines.
 Examples of polysaccharide vaccines include Meningococcal disease caused by Neisseria
meningitidis groups A, C, W135, and Y, as well as Pneumococcal disease.
2. Conjugated Vaccines
 These vaccines are prepared by linking the polysaccharides or sugar molecules on the outer
layer of the bacteria to a carrier protein antigen or toxoid from the same microbe.
 The vaccine that protects against Haemophilus influenzae type B (Hib) is a conjugate vaccine.
 Today, conjugate vaccines are also available to protect against pneumococcal and
meningococcal infections.
3. Toxoid Vaccines
 These vaccines are prepared from inactivated toxins, by treating the toxins with formalin, a
solution of formaldehyde, and sterilized water.
 This process of inactivation of toxins is known as detoxification and the resultant inactive
toxin is known as a toxoid.
 The toxins used for the preparation of toxoids are obtained from the bacteria that secrete the
illness-causing toxins.
 Examples of toxoid vaccines include diphtheria and tetanus toxoid vaccines.
 4. Recombinant Protein Vaccines
 After the start of the generic engineering era, recombinant DNA technology also evolved. This
is where DNA from two or more sources is combined. This technology harnessed the
development of recombinant protein vaccines.
 For recombinant vaccines to induce immunity against a pathogen, they have to be administered
along with an adjuvant or expresses by a plasmid or a harmless bacterial or viral vectors.
 Production of these recombinant protein vaccines involves the insertion of DNA encoding an
antigen such as a bacterial surface protein, which stimulates an immune response into bacterial
or mammalian cells, expressing the antigen in these cells, and then the antigen is purified from
them.
 The classical example of a recombinant protein vaccine currently in use in humans is the
vaccine against hepatitis B. The vaccine antigen is a hepatitis B virus protein produced by
yeast cells into which the genetic code for the viral protein has been inserted.
 Vaccines that are also used to prevent human papillomavirus (HPV) infections are also based
on the recombinant protein antigens.
Nucleic Acid Vaccines (Third Generation Vaccines)
 These are vaccines designed to aim at introducing the genetic materials that code the antigen or
the antigen that is aimed at inducing an immune response, enabling the host cells to use the
genetic materials to produce the antigens.
 The advantages of the nucleic acid vaccine approach include:
 stimulating a broad long-term immune response
 excellent vaccine stability
 ease of large-scale vaccine manufacture
 rapid production
 reduces potential risks of working with the live pathogen
 encoding only the key antigen without including other proteins
1. DNA plasmid vaccines
 These are vaccines that are composed of a small circular piece of DNA known as a plasmid.
The plasmid carries genes that encode proteins from the pathogen of interest.
 Experimental DNA plasmid vaccines have been designed to address some viral disease threats
including SARS coronavirus (SARS-CoV) , H5N1 avian influenza , H1N1 pandemic influenza
and Zika virus.
2. mRNA vaccines
 mRNA is an intermediary between DNA and protein. Recent technological advances have
developed mRNA vaccines overcoming the instability issues of mRNA and its delivery into
the cells, with encouraging results.
 Some experimental mRNA vaccines have been designed to protect mice and monkeys against
Zika virus infection, and administered in a single dose.
3. Recombinant vector vaccine
 These are vaccines designed as vectors or carriers using harmless viruses or bacterium and
they introduce the genetic material into cells.
 Majorly these vaccines are designed and approved for use to protect animals from infectious
diseases, including rabies and distemper, but some have been developed to protect humans
from viruses such as HIV, Zika virus, and Ebola virus.