CHAPTER ONE
INTRODUCTION
1.0 Background of the Study
Immunization is the process by which an individual’s immune system becomes fortified against an agent (known as the immunogen). When this system is exposed to molecules that are foreign to the body, called non-self, it will orchestrate an immune response, and it will also develop the ability to quickly respond to a subsequent encounter because of immunological memory. This is a function of the adaptive immune system. Therefore, by exposing an animal to an immunogen in a controlled way, its body can learn to protect itself; this is called active immunization (Okwor, et al., 2012)
The most important elements of the immune system that are improved by immunization are the T cells, B cells, and the antibodies B cells produce. Memory B cells and memory T cells are responsible for a swift response to a second encounter with a foreign molecule. Passive immunization is direct introduction of these elements into the body, instead of production of these elements by the body itself. Immunization is done through various techniques, most commonly vaccination. Vaccines against microorganisms that cause diseases can prepare the body’s immune system, thus helping to fight or prevent an infection. The fact that mutations can cause cancercells to produce proteins or other molecules that are known to the body forms the theoretical basis for therapeutic cancer vaccines. Other molecules can be used for immunization as well, for example in experimental vaccines against nicotine (NicVAX) or the hormone ghrelin in experiments to create an obesity vaccine. Immunizations are definitely less risky and an easier way to become immune to a particular disease by risking a milder form of the disease itself. They are important for both adults and children in that they can protect us from the many diseases out there.
Through the use of immunizations, some infections and diseases have almost completely been eradicated throughout the United States and the World. One example is polio. Thanks to dedicated health care professionals and the parents of children who vaccinated on schedule, polio has been eliminated in the U.S. since 1979 (American Pharmaceutical Association [Apha], 2013). Polio is still found in other parts of the world so certain people could still be at risk of getting it. This includes those people who have never had the vaccine, those who didn’t receive all doses of the vaccine, or those traveling to areas of the world where polio is still prevalent.
Immunization is the most precious gift that a health care worker can give a child and it remains the most cost effective preventative health intervention presently known (South Africa, 2003; Cameroun, 2009). Vaccines are sensitive biological substances that gradually lose their potency with time (World Health Organization [WHO], 1998) and this loss of potency can be accelerated when stored out of the recommended range of temperature (WHO, 2004). Any loss of potency in a vaccine is permanent and irreversible. Consequently, a proper storage of vaccines at the recommended temperature conditions is vital so that vaccines’ potency is retained up to the moment of administration (WHO, 1998).
1.1 Type of Vaccines
Vaccines are dead or inactivated organisms or purified products derived from them. There are several types of vaccines in use (National Institute of Allergy and Infectious Disease, 2012). These represent different strategies used to try to reduce risk of illness, while retaining the ability to induce a beneficial immune response.
Inactivated Vaccines
Some vaccines contain inactivated, but previously virulent, micro-organisms that have been destroyed with chemicals, heat, radiation, or antibiotics. Examples are influenza, cholera, bubonic plague, polio, hepatitis A, and rabies vaccines.
Attenuated Vaccines
Some vaccines contain live, attenuated microorganisms. Many of these are active viruses that have been cultivated under conditions that disable their virulent properties, or that use closely related but less dangerous organisms to produce a broad immune response. Although most attenuated vaccines are viral, some are bacterial in nature. Examples include the viral diseases yellow fever, measles, rubella, and mumps, and the bacterial disease typhoid. The live Mycobacterium tuberculosis vaccine developed by Calmette and Guérin is not made of a contagious strain, but contains a virulently modified strain called “BCG” used to elicit an immune response to the vaccine. The live attenuated vaccine-containing the strain Yersinia pestis EV is used for plague immunization. Attenuated vaccines have some advantages and disadvantages. They typically provoke more durable immunological responses and are the preferred type for healthy adults. But they may not be safe for use in immunocompromised individuals, and may rarely mutate to a virulent form and cause disease
Toxoid
Toxoid vaccines are made from inactivated toxic compounds that cause illness rather than the micro-organism. Examples of toxoid-based vaccines include tetanus and diphtheria. Toxoid vaccines are known for their efficacy. Not all toxoids are for micro-organisms; for example, Crotalus atrox toxoid is used to vaccinate dogs against rattlesnake bites.
Subunit Vaccines
Protein subunitrather than introducing an inactivated or attenuated micro-organism to an immune system (which would constitute a “whole-agent” vaccine), a fragment of it can create an immune response. Examples include the subunit vaccine against Hepatitis B virus that is composed of only the surface proteins of the virus (previously extracted from the blood serum of chronically infected patients, but now produced by recombination of the viral genes into yeast), the virus-like particle (VLP) vaccine against human papillomavirus (HPV) that is composed of the viral major capsid protein, and the hemagglutinin and neuraminidase subunits of the influenza virus. Subunit vaccine is being used for plague immunization.
Conjugate Vaccines
Certain bacteria have polysaccharide outer coats that are poorly immunogenic. By linking these outer coats to proteins (e.g., toxins), the immune system can be led to recognize the polysaccharide as if it were a protein antigen. This approach is used in the Haemophilus influenzae type B vaccine
Experimental Vaccines
A number of innovative vaccines are also in development and in use, they include;
Dendritic cell vaccines
The combine dendritic cells with antigens in order to present the antigens to the body’s white blood cells, thus stimulating an immune reaction. These vaccines have shown some positive preliminary results for treating brain tumors (Kim and Liau, 2010) and are also tested in malignant melanoma (Anguille, et al., 2014).
Recombinant Vector
By combining the physiology of one micro-organism and the DNA of the other, immunity can be created against diseases that have complex infection processes