Immunity to diphtheria in the 3–19 year age group in Italy

Abstract In Italy, immunization with diphtheria toxoid has been compulsory for all newborns since 1939. The last two clinical cases of diphtheria were reported in 1987. During the period 1987–1989, immunity against diphtheria was assessed by neutralization test in a random sample of 1740 healthy subjects 3–19 years old, from five geographical areas of Italy. Of the total population, 76.5% showed antibody levels considered to be protective (⩾0.1 IU ml −1 ), 17.2% had a relative degree of protection (0.01–0.09 IU ml −1 ), and 6.3% lacked immunity ( −1 ). The percentage of unprotected subjects increased from 6.1% in the age group of 3–5 years to 11.4% in the age group of 18–19 years (p