This rate more than doubled during the 1980 's and the early 1990 's . Studies conducted by Fine and Clarkson have demonstrated that infection usually occurred in cycles every for 2 to 5 year periods . These cycles were roughly maintained before and after vaccination against Pertussis were introduced . Fine and Clarkson have suggested that vaccine may have controlled the development of the disease , but has not interfered or blocked transmission of the infection . Children are still transmitting the disease but...











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