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Necessity

When a vaccination program successfully reduces the disease threat, it may reduce the perceived risk of disease as cultural memories of the effects of that disease fade. At this point, parents may feel they have nothing to lose by not vaccinating their children. If enough people hope to become free-riders, gaining the benefits of herd immunity without vaccination, vaccination levels may drop to a level where herd immunity is ineffective. According to Jennifer Reich, those parents who believe vaccination to be quite effective but might prefer their children to remain unvaccinated, are those who are the most likely to be convinced to change their mind, as long as they are approached properly.