The Yale journal of biology and medicine
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Measles vaccine cannot give high sero-conversion rates in developing countries. The high birth rates characteristic of these countries lead to infection at a very early age, thus making it difficult to vaccinate before exposure to the disease. ⋯ During the period when vaccine is given at an early age, the titers in responding children will be low, and this will leave children of the next generation with little protection. It is important, therefore, that if vaccine is used early the program be intensively and consistently applied to control virus circulation before the next generation is born.