Vaccination and Immunization

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Chapter: Pharmaceutical Microbiology : Vaccination And Immunization

People rarely suffer from the same infectious disease twice. Reinfections normally occur, primarily (1) when the infectious agent exhibits antigenic plasticity such as with the common cold and influenza...


VACCINATION AND IMMUNIZATION

 

Introduction

 

People rarely suffer from the same infectious disease twice. Reinfections normally occur, primarily (1) when the infectious agent exhibits antigenic plasticity such as with the common cold and influenza; (2) if the patient is immunocompromised, due for example to immunosuppressive therapy or immunological disorders; or (3) when a significant amount of time has passed after the first infection. Alternatively, the patient may have failed to eliminate the primary infection which remained latent and emerged later in a modified of similar form as for example with herpes simplex (oral and genital herpes), herpes zoster, (chickenpox) and HIV/AIDS.

Immunity against reinfection was recognized long before the discovery of the causal agents of infectious disease. Consequently, efforts were made towards developing treatment strategies that could generate immunity to infection without the individual suffering the infection. An early development was the attempted prevention of smallpox (variola major) through the dermal inoculation of healthy individuals with material taken from active smallpox lesions. Such treatments often produced single localized lesions and commonly, but not always, protected the recipient from contracting full-blown smallpox. The process became known as variolation and, unknown to its practitioners, protected against the disease by changing the route of infection of the causal organism from respiratory transmission to cutaneous. Unfortunately, occasional cases of smallpox resulted from such practices and variolated individuals could also (rarely) infect others, resulting in infection. Further developments recognized that immunity developed towards one pathogen may be associated with cross-immunity towards related infectious agents. Cowpox is a disease of cattle that can be transmitted to humans. The symptoms are similar to those of smallpox, but considerably less severe. Following the observation that individuals exposed to cowpox were conferred protection against smallpox, Edward Jenner substituted material taken from active cowpox (vaccinia) into the variolation procedures. This conferred much of the protection against smallpox that had become associated with variolation but without the associated risks. This discovery, made over two centuries ago, became known as vaccination and heralded a new era in disease control. The term vaccination was originally used to refer to prophylactic measures that use living microorganisms or their products to induce immunity, but the term is now used to refer to all immunization procedures.

Vaccination is used to protect individuals against infection and also to protect communities against epidemic disease. Such public health measures have met with spectacular success and in instances where there is no reservoir of the pathogen other than in infected individuals and survival of the pathogen outside the host is therefore limited, vaccination has the potential to eradicate the disease permanently. This has already been achieved for smallpox where the coordinated deployment of an effective vaccine over many decades led to the eradication of this disease. The global eradication of smallpox was endorsed by the World Health Assembly on 8 May 1980. Another candidate disease for global eradiation by vaccination is poliomyelitis, where effective vaccination programmes have reduced the annual incidence to fewer than 2000 cases. The virus persists, however, in India, Pakistan, Afghanistan and Nigeria. The Global Polio Eradication Initiative, spearheaded by the World Health Organization (WHO), Rotary International, the U.S. Centers for Disease Control (CDC) and the United Nations Children’ s Fund (UNICEF) is now actively working towards the eradication of this virus. It has been calculated that eradication is a more cost-effective option than containing the disease, as well as reducing morbidity associated with the residual cases. The effectiveness of poliomyelitis vaccines is clearly indicated by data shown in Figure 10.1.

 


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