Vaccination programmers.

Vaccination programmers

                                      Children in the UK can be given a series of vaccine to protect them against a range of disease (P1). In some countries vaccination is a legal requirement. Vaccination programmers have been particularly successful in virtually eliminating polio (poliomyelitis) and diphtheria in develop countries. Polio my soon become extinct worldwide. Diphtheria is vary rate in the UK, reduced to only 13 cases and no death between 1986 and 1991.

By 1984 the world health organization’s programme of vaccination, which is targeted against six major diseases (measles, pertussis,[whooping, cough], tetanus, polio, tuberculosis, diphtheria) had immunized some 50% of the children in the world and this has risen to 80% by the mid 1990. It has been estimated that this programme prevented more than one million deaths annually between 1974 and 1984. However, despite great progress, by 1990 about 3 million were still dying each year from these diseases and about 4.6 million were still fully vaccinated. Measles was killing 1.4 million annually (one every 20 seconds). Another 490,000 died of pertussis annually and 450,000 of TB. The manual cost, one-third of which is given in aid, is about US$1.5 thousand million.

       The world health organization expanded programme of  Immunization (EPI) aims to immunize more than 90% of the world’s new born against  a number of viral and bacterial diseases by the year 2000. Hepatitis B is now also being targeted and it is hoped to eradicate polio by the year 2000.

             There is still a need for new vaccines, for example against malaria, dengue fever, sleeping sickness, warm infection, HIV, leprosy and others. Not only are new vaccines required, also more effective and safer vaccines than those in used at the present time are needed. For example the vaccine for cholera is only effective in 50% of patents and the duration of immunity is relatively short. The flu vaccine also needs improvement to make it more effective.

Type of vaccine

         The different types of vaccine are described in section type of vaccination. There has been much debate about the relative merits of live and killed vaccines. Generally speaking, live vaccines are more effective although in the past they have been more risky. Other factor such has cost, safely, politics and social acceptance can determine whether there is high uptake of a particular vaccine and whether successful.

        There are many approaches to making and using a vaccine. For example in the UK three different vaccines have been licensed for typhoid vaccination.

     1. A killed whole cell vaccine (no longer available),

     2. A polysaccharide extract from the capsule of the typhoid bacterium.

     3. A live attenuated string of the typhoid bacterium, salmonella typhi.

               The second one is the most recent, having been introducing in 1992. It requires the least number of does and is the most preferred.

   The most important issue for developed countries is the safety of the vaccine, whereas in a developing country the question of cost and how to deliver the vaccines are probably of greater importance.

    A relatively recent development in the production of vaccine is that of using genetic engineering techniques. Many pathogens cannot be cultured outside their natural host. Thus the conventional approaches to vaccination cannot be used. For example, the microbe causing human syphilis (treponema pallidum) and the bacterium that causes leprosy (mycobacterium leprae) have never been grown in vitro (outside the body). Thus is not possible to generate live attenuated or inactivated vaccine by culturing techniques. In these examples recombinant DNA technology offer an alternative approach, allowing genes for antigens to be transferred from these organisms to more useful hosts such as E. coil, yeast or mammalian cells. These can then be used to produce bulk quantities of antigens for vaccines. For example, the surface antigen gene of hepatitis is simple to identify, clone and express. However, not all protective antigens are as simple to develop.  

    

Safety and effectiveness of vaccines

       There is sometimes public controversy regarding the effectiveness of vaccines. Up to 1986,160 million doses of measles vaccine (a live attenuated virus) had been administered in the UK, with an excellent record of protection. Of the children given vaccination, 5-15% developed fever on the fifth day, lasting several days. One recipient of vaccine in one million developed a disorder of the central nervous system know as encephalitis. This can cause extreme concern in parents when these facts appear in newspaper just as vaccination campaigns begin. The chances of this complication from measles vaccination are, in fact, less than the incidence of encephalitis from an unknown origin. Whooping cough (pertussis) vaccine, which contains dead bacteria, sometimes has a rare neurological adverse reaction resulting in convulsions and brain damage. This occurs once in about 100000 doses and the possibility of permanent brain damage occurs once in 300000 doses. Both measles and diphtheria vaccines can have local reactions of inflammation and laryngitis. However, deaths from these diseases still occur amongst unvaccinated children and parents must weigh up the information and take the responsibility of deciding whether or not to have their children vaccinated.     

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