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Explanation. This graph shows the number of notified cases per year from 1956 onwards. The start is roughly when all infants were given pertussis vaccine as routine. Levels fell and remained low until the vaccine scare that started in 1974 and was followed by a resurgence of the disease that lasted 12 years. An interesting feature is the different notification rates in the early seventies and mid nineties, when the immunization rates were very similar (about 90%). I believe this is partly explained by the ability of doctors to recognize the disease. Those practising in the seventies were very familiar with it, but not those in the nineties, so it gets missed.