<prompt> Commonest age group for diptheria is -1-2 Years1-5 Years2-7 Years2-9 Years  <response>: Diphtheria paicularly affects children aged 1 to 5 yrs. In countries where widespread immunization practised, a shift in age incidence has been observed from preschool to school age. Ref:PARK;S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition , Page :160 