The benefits of immunization programs are beyond prevention of specific diseases in individuals. Efficacious vaccine not only protects the immunized, but also extends their benefits to unimmunized individuals of the community through “herd protection” or “herd immunity”. Herd immunity is the basis on which all national immunization programs are designed. It is defined as the resistance of a group of people to an attack by a disease to which a large proportion of the members of the group are immune. The percentage of the population that must however be immunized depends on three factors: the infectivity of the disease, the vulnerability of the population, and environmental factors. The aim of herd immunity is to reduce effective reproduction rate to less than 1 for each disease thus barring the disease propagation in community. Herd immunity has been found to be effective in multiple respiratory and diarrheal diseases. To conclude, no vaccine offers complete protection, but the spread of disease from person-to-person is much higher in those who remain unvaccinated. Herd immunity can definitely protect the susceptible individuals from acquiring the infection if the numbers of immunized individual are above the threshold level. It is an achievable goal for majority of the communicable diseases and all efforts should be taken by the program managers to amplify it in the community.
Key words: Herd İmmunity, Vaccine, Effective Reproduction Rate, Communicable Disease Article Language: Turkish English
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