Immune system, Vaccination and herd immunityThe Immune system

1- Innate Immune System :

First-line defense: physical and chemical barrierThe first-line defense includes barriers to infection, such as skin and mucus coating of the gut and airways. Second-line defense: Phagocytic cellsphagocytic cells (Myeloid cells) (macrophages and neutrophil granulocytes) can destroy (phagocytose) foreign substances. Phagocytosis involves digestion of the bacterium by using enzymes.2- The Adaptive Immune system: A- Humoral immune system: -> acts against bacteria and viruses using immunoglobulins (also known as antibodies) -> produced by B cells. B- Cellular immune system: -> destroys intracellular pathogens (such as virus-infected cells and mycobacteria causing tuberculosis) using T cells (also called "T lymphocytes"; "T" means they develop in the thymus).Active ImmunityA- Protection produced by the person's own immune systemB-Usually permanent.Passive Immunity

A- Protection transferred from another person or animal B-Temporary protection that wanes with timeAntigen

A live or inactivated substance (e.g., protein, polysaccharide) capable of producing an immune responseAntibody

Protein molecules (immuno-globulin) produced by B lymphocytes to help eliminate an antigen Passive Immunity

Transfer of antibody produced by one human or other animal to another Temporary protection Transplacental most important source in infancy Vaccination Vaccination is a method of giving antigen to stimulate the immune response through active immunization. A vaccine is an immuno-biological substance designed to produce specific protection against a given disease. A vaccine is antigenic but not pathogenic. Immunity and immunologic memory similar to natural infection but without risk of disease Types of vaccines Live vaccines Attenuated live vaccines Inactivated (killed vaccines) Toxoids Polysaccharide and polypeptide (cellular fraction) vaccines Surface antigen (recombinant) vaccines. Live vaccines Live vaccines are made from live infectious agents without any amendment. The only live vaccine is Variola small pox vaccine, which is not pathogenic but antigenic, giving cross immunity for variola.Polysaccharide and polypeptide (cellular fraction) vaccines

They are prepared from extracted cellular fractions e.g. meningococcal vaccine from the polysaccharide antigen of the cell wall, the pneumococcal vaccine from the polysaccharide contained in the capsule of the organism, and hepatitis B polypeptide vaccine. Their efficacy and safety appear to be high.Surface antigen (recombinant) vaccines. It is prepared by cloning HBsAg gene in yeast cells where it is expressed. HBsAg produced is then used for vaccine preparations. Their efficacy and safety also appear to be high.Barriers to Immunizations Coverage: Improving immunization coverage requires examination of reasons that children are not immunized. Many barriers exist. They include religious, financial, social, and cultural factors; philosophical objections; and provider limitations. Global Trends:

During ht last several decades, substantial progress has been made in controlling some major infectious diseases around the world, although other diseases have not been managed as well. The following are some of the major accomplishments: The WHO's Expanded Program on Immunization (EPI) was launched in 1974. as a result, by 1995, more than 80% of the world's children had been immunized against diphtheria, tetanus, whooping cough, poliomyelitis, measles, and TB, compared with fewer than 5% in 1974 (WHO, 1998) Global eradication of smallpox was achieved in 1980. In 1988, a campaign for global eradication of poliomyelitis by the year 2000 was launched. Reported cases worldwide have declined by 99% since the campaign began. The global threat of plague has declined in the last 40 years, largely as a result of the use for antibiotics and insecticides. Some major problem communicable diseases and areas remain, including the following: Malaria remains a major threat, even though the mortality rate has improved in the last 25 years. Cholera was mainly confined to Asia in the early 20th century through improvements in sanitation elsewhere. However, a series of pandemics have affected much of the world since 1960 and have become more widespread and more frequent in Africa since 1970s. TB has made a powerful resurgence in the last 3 decades as many countries let their control programs become complacent. WHO declared TB a global emergency in 1993. Disease Control :The term disease control describes ongoing operations aimed at reducing:

The incidence of disease The duration of disease and consequently the risk of transmission The effects of infection, including both the physical and psychosocial complications The financial burden to the community. Control activities focus on primary prevention or secondary prevention, but most programs combine both.

Disease Elimination

Between control and eradication, an intermediate goal has been described, called "regional elimination" The term "elimination" is used to describe interruption of transmission of disease, as for example, elimination of measles, polio and diphtheria from large geographic regions or areas Regional elimination is now seen as an important precursor of eradicationDisease Eradication

It is the process of Termination of all transmission of infection by extermination of the infectious agent through surveillance and containment. Eradication is an absolute process, an "all or none" phenomenon, restricted to termination of an infection from the whole world. It implies that disease will no longer occur in a population. To-date, only one disease has been eradicated, that is smallpox. Herd Immunisation

immunisation against various deadly diseases is an important preventive measure which the doctors recommend right from the birth. Behind the program schedule of vaccination there is a definite science and policy and such preventive measures help in the long run to protect the whole human community from diseases and infections. When non immunized people live with community of people who are immunized they are indirectly protected from getting inflicted from any disease. This is called as herd immunity or community immunity. According to herd immunity theory when sufficient amount of people in a particular group or community is immune to a certain type of disease, it acts as a barrier for other non immunized people as well. Due to this people who are not vaccinated too are protected. High herd immunity reduces the probability that the few unimmunized parsons will come in contact with one another, making spread of the disease less likely. Outbreaks may occur if the immunization rate falls to less than 85% (scutchfield & Keck, 2001) or if unimmunized susceptible persons are grouped together rather than dispersed throughout the immunized community. An example of lack of herd immunity is presented in the Global Community. 1