<prompt> Pertusis affects which age2355710 years  <response>: In prevaccine era, and in countries where immunization is limited the peak incidence of pertussis is in children 1-5 years of age, infant accounts for 15 of cases.In recent years, where vaccination is employed, approximately one half of cases have occurred in infants younger than 1 year of age and one fourth in adolescent and adults. 