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Vaccines and How They Work Vaccines and How They Work Vaccines and How They Work Npi Reference Guide on Vaccines and Vaccine Safety 5 VACCINES AND HOW THEY WORK VACCINES AND HOW THEY WORK VACCINES AND HOW THEY WORK NPI REFERENCE GUIDE ON VACCINES AND VACCINE SAFETY 5 GLOSSARY TERMS VACCINES AND HOW THEY WORK Acquired immunity Immunization Acute Influenza Infectious Diseases Antibody Innate immunity Antigen Lymphocytes Infectious diseases have been the bane of human existence throughout history. Association Macrophage Evidence of infection has been found in mummified remains from ancient Egypt1 Asthma Measles 2 Attenuated vaccines Mumps and elsewhere, and in the oral and written histories of all cultures. The Black Death Autoimmune disease Neisseria meningitidis of the Middles Ages,3 the decimation of the native peoples of the Americas by B cell Neonate imported disease4 and the worldwide influenza epidemic of 19184 are vivid reminders Bacteria Pathogens Booster Pentavalent vaccine that infectious diseases have profoundly shaped our world and have the potential to Bordetella pertussis Pertussis do so again. Cases Pneumococcal disease Causal association Pneumococcal polysaccharide Infectious diseases are caused by organisms that are able to exploit the human body Cell-mediated response Pneumonia so that they may grow and reproduce. In general, these organisms are tiny and can Chemokines Polysaccharide Chickenpox Polysaccharide vaccine exist in our lungs, blood or other body tissues and organs. They gain access to us Chronic Protein through the air we breathe, the food and water we ingest, or damage to our skin. Clostridium tetani Rabies Disease-causing agents (pathogens) include bacteria and viruses.5 Combination vaccine Recombinant DNA technology Conjugate vaccine Risk Bacteria are tiny and can be seen only with the aid of a microscope. They typically Corynebacterium diphtheriae Rubella are rod-shaped or round (see table below). Exposure to these pathogens occurs either Cytokines Smallpox Cytotoxic T cell Specific acquired immunity by inhalation or oral uptake. However, exposure to the bacteria that cause tetanus is Diabetes Streptococcus pneumoniae more commonly associated with puncture or laceration injuries or other damage to Diphtheria Subunit vaccines the skin, and the disease symptoms result from a toxic chemical (toxin) that the Disease T cell Dysfunction Tetanus bacteria produce and release. The diseases caused by the bacteria listed in the following Epidemic Toxin table can be prevented by vaccines licensed for use in the US. German measles Type 1 diabetes Haemophilus influenzae type b Vaccine Helper T cell Vaccine schedule Bacteria Bacteria Shape Disease Bacteria Causes Hepatitis Valent Hepatitis A Varicella Corynebacterium diphtheriae Rod Diphtheria Hepatitis B Virus Clostridium tetani Rod Tetanus Hexavalent vaccine White blood cells Bordetella pertussis Rod Pertussis Haemophilus influenzae type b Rod Hib disease ACRONYMS Neisseria meningitidis Round Meningococcal disease Streptococcus pneumoniae Round Pneumococcal disease DNA Deoxyribonucleic acid Hib Haemophilus influenzae type b IOM Institute of Medicine MHC Major histocompatibility complex Viruses are smaller than most bacteria, can be seen only with an electron micro- scope and are much simpler in terms of their biochemical composition and biological activity. Viral diseases that can be prevented by vaccines licensed for use in the US include hepatitis A, hepatitis B, polio, influenza, measles, mumps, rubella (German WEB RESOURCES measles) and varicella (chickenpox). Upon infection, viruses typically enter individual American Institute of Immunology cells that make up the target tissue, e.g., the hepatitis A and hepatitis B viruses enter http://library.thinkquest.org/12429/welcome.html cells of the liver. Because viruses lurk within the cells of the body, the development Cells Alive of anti-virus vaccines employs strategies different from those used in the development http://www.cellsalive.com of vaccines against bacterial pathogens. These differences are described below. Dalhousie University Medical Center http://www.medicine.dal.ca/micro/education/pimunit/home.htm Davidson College Exposure to Pathogens http://www.bio.davidson.edu/courses/immunology/bio307.html Bacteria and viruses are found everywhere in our environment6 and cannot be Garland Publishing avoided. Most cause no health problems and some are even beneficial, such as those http://blink.uk.com/immunoanimations that live in the human intestine and aid the digestive process. Some, such as those National Cancer Institute http://newscenter.cancer.gov/sciencebehind/immune/immune00.htm mentioned above, clearly cause disease, while others occasionally may be responsible University of California, San Diego for disease in certain individuals. Disease results when a pathogen becomes estab- http://wilson-squier.ucsd.edu/research/sb/ve/immunology lished in a person and is associated with damage to host tissues as a consequence of University of Leicester its growth and reproduction, or the release of toxins.7 This occurs in two steps: the http://www-micro.msb.le.ac.uk/312/BS312.html host must first be exposed to the pathogen, and secondly, infection must occur. While IMMUNIZATION SCHEDULES scientists agree that disease develops as a result of this process, the required amount Childhood schedule of the pathogen that the body must be exposed to in order for infection to result is http://www.cdc.gov/nip/recs/child-schedule.htm#printable Adult schedule much debated. Indeed the majority of infections do not result in disease. http://www.cdc.gov/nip/recs/adult-schedule.htm 6 NPI REFERENCE GUIDE ON VACCINES AND VACCINE SAFETY VACCINES AND HOW THEY WORK Exposure to a single pathogenic bacterial cell is considered by When a pathogen or vaccine enters the body through inhala- some to be sufficient to result in infection and disease8 if it is tion, ingestion, a wound or injection, the cells in the surrounding able to evade all of the body’s natural defenses (described below) tissues release chemicals called chemokines and cytokines that that protect a person from infection. If this occurs, that single attract various types of white blood cells to the area of injury, 16 cell will be able to grow and divide, ultimately giving rise to leading to the destruction of the pathogen. White blood cells sufficient numbers of daughter cells to trigger disease. However, are found in everyone’s blood and are responsible for keeping our the development of disease following infection is more likely to bloodstream and tissues free of pathogens, abnormal cells and occur if the host is exposed to large numbers of pathogens versus other unwanted material. Several types of white blood cells are a single cell. Hence, disease is more likely to occur if the person critical to the natural immune response. One type of white blood is exposed to 10,000 pathogenic bacteria than if exposed to cell is called a macrophage. It is among the first of the responding cells to arrive at the site of injury where it engulfs and destroys 1,000 or 100 bacteria. the pathogen. Natural Defenses Against Infection Other types of white blood cells, called lymphocytes, also are Human beings are protected against infectious diseases by attracted to the site. These cells, along with the macrophages various physical and biochemical factors.9-11 Our first level of release other chemokines and cytokines that direct the immune protection against disease is our skin and its acidic secretions, response. The local accumulation of the various types of cells tears and the mucous membranes that line our nose, mouth and contributes to the inflammation or redness that is often observed at sites of infection and injury. These cells and processes consti- other passages connecting our internal and external environ- tute the natural immune response and are often sufficient to clear ments. These factors and others, when functioning properly, or eliminate the infection. keep pathogens at bay. Innate immunity is neither specific nor long lasting. This response If an infectious agent, a pathogen, gets past the first line of occurs each time there is a threat of infection, and is virtually defense, our bodies have a second tier of defense provided by 12-14 identical for each pathogen that gains entry. Natural immunity is natural or innate immune mechanisms. In this case, our also independent of the number of times a person is exposed to own cells and the chemicals they produce seek out, identify and any single agent, that is, even if a person is exposed to a single eliminate the pathogen. These very general and non-specific agent many times, their response to each exposure is the same. responses are critical to the maintenance of good health. On occasion, a pathogen can get past our bodies’ primary Acquired Immunity – Antibody Response protective mechanisms if it is present in very large numbers or if Induction of a specific, protective immune response, i.e., it has evaded or suppressed these processes. Stronger protection acquired immunity, enhances the natural response by directing is needed, and we respond by mounting an acquired immune certain interactions among the cells participating in the immune reaction specific to the pathogen. These responses involve a response. Conditions for these interactions are met when the variety of types of cells found in the blood and tissues and can number of pathogens is large or when the pathogens are not require a week or more to become established. Acquired immunity readily eliminated by the natural mechanisms. consists of antibody and cell-mediated responses. Macrophages play a critical role in the establishment of specific acquired immunity.10,11 (See Figure 1 below.) As macrophages An acquired immune response can result in either short-term engulf an infectious organism or a certain vaccine, the organism or long-term protection against a specific pathogen and, per- haps, against some of its close relatives. In the case of long- Figure 1 term protection, re-exposure to the same pathogen weeks, months or years later reactivates the response mechanisms laid down during the original exposure. This reactivation leads to rapid, effective elimination of the agent, often without clinical symptoms or signs of infection.
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