4- immunization against diseases of public health importance
A: THE BENEFITS OF IMMUNIZATION
Vaccines—which protect against disease by assuring immunity—are widely and routinely given around the world. This practice is based on the idea that it is better to keep people from falling ill than to focus only on helping them recover once they are ill. Suffering, disability, and death are avoided. Immunization is thought to prevent two to three million childhood deaths each year. In addition, infection is reduced, strain on health-care systems is eased,and money is frequently saved that can be used for other health services.
Immunization is a proven tool for controlling and even eradicating disease. An immunization campaign carried out by the World Health Organization (WHO) from 1967 to 1977 eradicated the natural occurrence of smallpox. When the program began, the disease still threatened 60% of the world's population and 20 killed every fourth victim. Eradication of poliomyelitis is within reach. Since the launch by WHO and its partners of the Global Polio Eradication Initiative in 1988, infections have fallen by 99%, and about five million people 25 have escaped paralysis. Between 2000 and 2008, measles deaths dropped worldwide by almost 78%, and some regions have resolved to eliminate the disease.
B: GLOBAL IMMUNIZATION COVERAGE
Coverage has greatly increased since WHO'S 30 Expanded Program on Immunization began in 1974, and the results are encouraging (Table 1). In 2009, global DTP3 (three doses of the diphtheria-tetanus-pertussis combination vaccine) coverage was 82%—up from 20% in 1980. However, millions of children worldwide were not reached by DTP3 in 2009, including many in South Asia and sub-Saharan Africa.
C: NEW VACCINES
Numerous new vaccines with major potential for improving health in developing countries have been produced since 2002. Incidence of meningitis, rotavirus, and pneumococcal disease, which killed millions of children annually (Table 2), has fallen in areas where the new vaccines have been introduced.
D: HISTORY
Introducing a small amount of smallpox virus by inhaling through the nose or by making a number of small pricks through the layers of skin (variolation) to create resistance to the disease began in the 10th or 11th century in Central Asia. Variolation was introduced into England in 1721. There, in 1798, Edward Jenner began treatments against smallpox, I the first systematic effort to control a disease through immunization.
In 1885. Louis Pasteur developed the first vaccine to protect humans against rabies. Vaccines against diphtheria and tetanus were introduced in the early 1900s, the Calmette- Gu6rin vaccine (against tuberculosis) in 1927, the Salk polio vaccine in 1955, and vaccines against measles and mumps in the 1960s.
E: HOW VACCINES WORK
Vaccines typically provide the immune system with harmless copies of an antigen: a portion of the surface of a bacterium or virus that the immune system recognizes as "foreign. " A vaccine may also provide a non-active version of a toxin—a poison produced by a bacterium—so that the body can create a defense against it.
Once an antigen is noticed by the immune system, white blood cells called B-lymphocytes create a protein called an antibody that is designed to attach to that antigen. Many copies of this antibody are produced. If a true infection of the same disease occurs, still more antibodies are created, and as they attach to their targets they may block the activity of the virus or bacterial strain directly, thus fighting infection. In addition, once in place, the antibodies make it much easier for other parts of the immune system to recognize and destroy the invading agent.
Immune systems are designed to "remember. " Once exposed to a particular bacterium or virus, they retain immunity against it for years, decades, or even a lifetime. This means they are prepared to quickly defeat a later infection. This is a huge benefit because a body encountering a germ for the first time may need from seven to twelve days to effectively defend it, and by then serious illness and even death may occur.
F: EFFECTIVENESS AND SAFETY
All vaccines used for routine immunization are very effective in preventing disease, although no vaccine attains 100% effectiveness. More than one dose of a vaccine is generally given to increase the chance of developing immunity.
Vaccines are very safe, and side effects are minor—especially when compared with the diseases they are designed to prevent. Serious complications occur rarely. For example, severe allergic reactions result at a rate of one for every 100.000 doses of measles vaccine. Two to four cases of vaccine-associated paralytic polio have been reported for every one million children receiving oral polio vaccine.
G: COST-EFFECTIVENESS OF IMMUNIZATION
Immunization is considered among the most cost-effective of health investments. There is a well-defined target group; contact with the health system is only needed at the time of delivery; and vaccination does not require any major change of lifestyte.
A recent study estimated that if the coverage for the pneumococcal disease vaccine reached the levels of DTP3 coverage in Latin America and the Caribbean, it would prevent over half of all cases of the disease and about 9,500 deaths annually. This could be achieved at a cost of as low as 62 U.S. dollars per life saved. The cost of the immunizations is clearly compensated for by its life-saving value. THE
H: DECADE OF VACCINES
The effort to increase immunization coverage around the world is continuing with the Global Vaccine Action Plan. This plan promotes the discovery and development of vaccines as well as their delivery to the world's poorest countries. The aim is to prevent the deaths of millions of children over the next decade.
