immune for life. Indeed, certain antigens can induce a robust immune response that is

maintained over a long period. However, for most vaccines, immunity starts waning

after a certain period. At this point it is important to administer a booster which can

stimulate both the B- and T-cell populations specific to the pathogen.

3.4.1

VACCINE DESIGN

Key to the success of a vaccination strategy is the design of the antigen and several

common strategies are outlined in Figure 3.14. For instance, to create a response

that is as close as possible to the infection, it would be best to inject the same

pathogen, but in an attenuated state so that it cannot induce severe illness.

Alternatively, the pathogen can be inactivated or killed. In this case it will not

replicate, reducing the amount of antigen in the system and therefore the response.

Going a step forward, it is possible to identify a part of the pathogen that can

elicit a response that can protect the individual from the infection. This is called a

subunit vaccine. The subunit could be a protein, purified by fractionation of the

pathogen, or produced as a recombinant [8].

When a vaccine is developed, it must be tested, and part of that test measures

efficacy, the ability of the response to neutralize the effect of the pathogen. An

important element of the response is the production of antibodies and such anti-

bodies are referred to as neutralizing antibodies. Although most antibodies devel-

oped during vaccination are protective, it is important to be aware of and test for

FIGURE 3.14 Types of vaccines. This figure shows the different strategies that are used to

generate the antigen for a viral vaccine. It can be the virus, itself, either in an attenuated or

inactivated form. It can also be a component of the virus and this is referred to as a subunit

vaccine. The subunit vaccine can be delivered as a protein, or in the form of a nucleic acid

(DNA or RNA) fragment that codes for the subunit. The subunit can also be delivered by a

viral vector.

Introduction to basic immunology

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