Medical Microbiology: Vaccination - Essay Example

Medical microbiology- vaccination Immunity to infectious microorganisms can be achieved by active or passive immunization. In each case, immunity canbe acquired either by natural processes (usually by transfer from mother to fetus or by previous infection by the organism) or by artificial means such as injection of antibodies or vaccines. The agents used for inducing passive immunity include antibodies from humans or animals, whereas active immunization is achieved by inoculation with microbial pathogens that induce immunity but do not cause disease or with antigenic components from the pathogens (Jawetz, p.111). Vaccines play a special role in the health and security of nations. The World Health Organization (WHO) cites "immunization and the provision of clean water as the two public health interventions that have had the greatest impact on the world's health", and the World Bank notes that "vaccines are among the most cost-effective health interventions available". Over the past century, the integration of immunization into routine health care services in many countries has provided caregivers with some degree of control over disease-related morbidity and mortality, especially among infants and children. Despite these extraordinary successes, vaccines and their constituents (e.g., the mercury compound thimerosal, formerly used as a preservative) have come under attack in some countries as causes of neurodevelopmental disorders, such as autism and attention-deficit hyperactivity disorder; diabetes; and a variety of allergic and autoimmune diseases (Brown, p.181). Although millions of lives are saved by vaccines each year and countless cases of postinfection disability are averted, some segments of the public are increasingly unwilling to accept any risk whatsoever of vaccine-associated complications (severe or otherwise), and resistance to vaccination is growing (Jacobson, p. 3165) No medical procedure is absolutely risk-free, and the risk to the individual must always be balanced with benefits to the individual and to the population at large. This dichotomy poses two essential challenges for the medical and public health communities with respect to vaccines: (1) to create more effective and ever-safer vaccines, and (2) to educate patients and the general public more fully about the benefits as well as the risks of vaccine use (Ada, p.1043). Because immunity to infectious diseases is acquired only by infection itself or by immunization, sustained vaccination programs for each birth cohort will continue to be necessary to control vaccine-preventable infectious diseases until and unless their etiologic agents can be eradicated from every region of the world. An unwavering scientific and public health commitment to immunization is essential in countering public distrust and political pressure to legislate well-intentioned but ill-informed vaccine safety laws in response to the concerns of organized antivaccine advocacy groups. Ironically, it is the public health success of vaccines that has created a significant part of the problem: because the major fatal and disabling diseases of childhood are only rarely seen today in the United States, parents and young practitioners most likely will never have seen tetanus, diphtheria, Haemophilus influenzae disease, polio, or measles. Under these circumstances, the risks of immunization can easily (if erroneously) be perceived to outweigh the benefits, and this perception can be fueled by inaccurate information, poor science, and zealous advocacy. Caregivers must be prepared to educate parents about the importance of childhood immunization and to address their concerns effectively (Sears, pp.10) Vaccination of children is begun at about 2 months of age. The recommended program of childhood immunizations in this country, updated in 2006 by the American Academy of Pediatrics includes the following vaccines: Hepatitis B vaccine Diphtheria-pertussis-tetanus (DPT) combined vaccine (a recently developed acellular pertussis vaccine is recommended to replace the whole pertussis vaccine; the combined vaccine is now called DTaP) Trivalent (Sabin) oral polio vaccine (OPV) and inactivated (Salk) polio vaccine (IPV) Measles-mumps-rubella (MMR) combined vaccine Haemophilus influenzae (Hib) vaccine Varicella zoster (Var) vaccine for chickenpox Rotavirus (Rv) vaccine for infant diarrhea (new) Recommendations for vaccination of adults depend on the risk group. Vaccines for meningitis, pneumonia, and influenza are often given to groups living in close quarters (e.g., military recruits) or to individuals with reduced immunity (e.g., the elderly). Depending on their destination, international travelers are also routinely immunized against such endemic diseases as cholera, yellow fever, plague, typhoid, hepatitis, typhus, and polio. Immunization against the deadly disease anthrax had been reserved for workers coming into close contact with infected animals or products from them. Recently, however, suspected use of anthrax spores by terrorists or in biological warfare has widened use of the vaccine to military personnel and civilians in areas at risk of attack with this deadly agent (Stepanov, p. 155) Vaccination is not 100% effective. Instead, with any vaccine a small percentage of recipients will respond poorly and therefore will not be adequately protected .This is not a serious problem if the majority of the population is immune to an infectious agent. In this case, the chance of a susceptible individual contacting an infected individual is so low that the susceptible one is not likely to become infected .This phenomenon is known as herd immunity (reference). The appearance of measles epidemics among college students and unvaccinated pre-school - age children in the United States during the mid- to late-1980s resulted partly from an overall decrease in vaccinations, which had lowered the herd immunity of the population. Several factors must be kept in mind in developing a successful vaccine. First and foremost, the development of an immune response does not necessarily mean that a state of protective immunity has been achieved (Roitt, p.290). What is often critical is which branch of the immune system is activated, and therefore vaccine designers must recognize the important differences between activation of the humoral and the cellmediated branches. A second factor is the development of immunologic memory (Roitt, p. 290). For example, a vaccine that induces a protective primary response may fail to induce the formation of memory cells, leaving the host unprotected after the primary response to the vaccine subsides. The role of memory cells in immunity depends, in part, on the incubation period of the pathogen. In the case of influenza virus, which has a very short incubation period (1 or 2 days), disease symptoms are already under way by the time memory cells are activated. Effective protection against influenza therefore depends on maintaining high levels of neutralizing antibody by repeated re-immunizations (Donnelly, p. 583) For pathogens with a longer incubation period, demonstrable neutralizing antibody at the time of infection is not necessary. The poliovirus, for example, requires more than 3 days to begin to infect the central nervous system. An incubation period of this length gives the memory B cells time to respond by producing high levels of serum antibody. Thus, the vaccine for polio is designed to induce high levels of immunologic memory (Dove, 779). After immunization with the Salk vaccine, serum antibody levels peak within 2 weeks and then decline, but the memory response continues to climb, reaching maximal levels at 6 months and persisting for years (Roitt, p. 301). If an immunized individual is later exposed to the poliovirus, these memory cells will respond by differentiating into plasma cells that produce high levels of serum antibody, which protect the individual from infection. There are certain situations where vaccines should be used with care and caution. Such situations are breast feeding, situations of occupational exposure, HIV infections and other immune conditions and during travels abroad. Neither killed nor live vaccines affect the safety of breast feeding for either mother or infant. Breast-fed infants can be immunized on a normal schedule. Even premature infants can be immunized at their appropriate chronologic age. Seroconversion in response to hepatitis vaccine at birth may be impaired in some premature infants with birth weights of Read More