The third link in the chain of transmission is the susceptible host or people at risk. They may be protected by one or more of the following strategies:
One effective way of controlling the spread of infection is to strengthen the host defences, by means of active immunization, which is one of the most powerful and cost-effective weapons of modern medicine. There are some infectious diseases whose control is solely based on active immunization. e.g. polio, tetanus, diphtheria and measles. Vaccination against these diseases is given as a routine during infancy and early childhood, with periodic boosters to maintain adequate levels of immunity. Certain immunizations against some diseases are offered to high risk group or restricted to definite areas where disease is endemic or a public health problem eg. yellow fever.
Unfortunately vaccines are not available for every infectious disease (e.g. malaria, diarrheal diseases). Diseases for which improved or less costly vaccines are needed include tuberculosis, pertussis, meningococcal meningitis, hepatitis B, rabies, Japanese encephalitis, etc.
Immunization protects the greatest number of people. It reduces the number of susceptibles in the community, hence augments herd immunity, making the infection more difficult to spread. Further, it reduces the risk for those individuals who have escaped vaccination or those who have not developed satisfactory protection. But immunizations are not 100 per cent effective particularly when an individual is exposed to a large dose of pathogenic organisms.
Immunization schedule must be
Epidemiologically relevant that is vaccinations should be included only against public health problems having an effective vaccine
Immunologically effective: children must be vaccinated at an age when they are capable of forming defenses and have lost the antibodies transmitted by the mother. Importantly, children must be vaccinated at the right time that is before they are exposed to possible infection. An immunization may not be effective if given within too short an interval between subsequent doses
Operationally feasible: this includes cost and ability to achieve a high percentage of coverage which is a key factor in an effective immunization programme. The schedule must also minimize the number of visits by simultaneous administration of vaccines
Socially acceptable: the schedule must take into account the local customs, beliefs and practices, seasonal and climatic factors and daily work pattern of the community.
It is a short term expedient
Duration of immunity induced is short and variable
Undesirable reactions may occur
Has limited value in mass control of diseases
Hence it is recommended for non immune persons only when exposure to infection has just occurred or is imminent in the next few days.
Immunoglobulins should not be given within 3 weeks before or until 2 weeks after administration of a live attenuated vaccine. However, there are exceptions to this rule as in case of Hepatitis B where vaccine and immunoglobulins are administered simultaneously.
Non Specific Measures
Improvement in quality of life.
Legislative measures to formulate integrated programme and permit its effective implementation.