Vaccines are preparations of biological solutions or agents that are capable of conferring active immunity to human bodies against specific diseases. Vaccines are usually made from either weakened or dead forms of pathogens that causes diseases. Vaccines could also be prepared from the proteins of such pathogens or from their toxins. Vaccines are specific in their actions and are usually employed against infectious diseases and not against hereditary or non-infectious diseases.

Historically, the first vaccine was prepared by Edward Jenner in 1798. Jenner’s vaccine consisted of cowpox pathogen and was employed against smallpox. Vaccines basically work by instigating bodily reactions against the presence of pathogens that causes diseases, the proteins or toxins of these pathogens and then inducing the body’s immune system to make a record of it against future infection. Since the introduction of vaccines, their effects and activities have helped in curtailing the spread of infectious diseases worldwide and have even led to the eradication of some diseases.

Types of Vaccines

Several types of vaccines exist and each of them represents a different approach to creating an effective immune response to infections. Some vaccines are prepared by inactivating virulent microorganisms. These virulent pathogens are usually de-activated by either heat, radiation or by the use of antibiotics. Such vaccines are known as inactivated vaccines. Examples of inactivated vaccines include those used for influenza, poliomyelitis, and rabies.

Non-inactivated vaccines are of several types. One of these is described as attenuated vaccine. Attenuated vaccines usually contain virulent microorganisms that have been rendered impotent or less potent by disabling their virulent powers. Most of these contain disabled virulent viruses but a few contain bacteria that have been so treated. Yellow fever, mumps and measles are examples of attenuated viral diseases that have attenuated vaccines while typhoid is bacterial disease that has this type of vaccine. Some attenuated vaccines contain similar but less dangerous strains of the disease causing pathogen. Toxoid vaccines are made from toxins of disease-causing pathogens rather than the pathogens themselves. Examples are the vaccines used for tetanus and diphtheria. Sometimes, a part of the disease-causing agent rather than the whole may be used to prepare a vaccine. Such vaccines are referred to as sub-units. Other types of vaccines such as conjugates, valence and heterotypic vaccine also exist. Some vaccines are currently under development and are referred to as experimental vaccines.

Factors that affect the Effectiveness of Vaccines

The effectiveness of vaccines made be hampered by some factors. For example, some people’s immune system may show no response to the vaccine at all. This may be as a result of some medical conditions such as the use of some hard drugs. Age is also a factor just as genetic factors play a part. Also, several strains of a pathogen may exist and some of them may be resistant to the vaccine.


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