The catarrhal phase lasts ~ a week and is characterised by the development of a dry, unproductive cough.The paroxysmal phase may last for a month or more and is characterised by coughing fits, whooping, andpost-tussive vomiting. The person may be relatively well between paroxysms.The convalescent phase may last an additional 2 months or more, and is characterised by gradualimprovement in the frequency and severity of symptoms.