Serological immunity to diphtheria in Sweden in 1978 and 1984.

Antibody levels in relation to diphtheria toxin were studied in 2409 serum specimens collected from different age-groups in Sweden in 1977-78 and 1983-84. Among children and young adults less than 20 years of age, 46% showed antibody levels considered to be protective (greater than or equal to 0.1 IU/ml). The corresponding percentage among adults was 21%. In the child population, 35% showed a relative degree of protection (less than 0.1-greater than or equal to 0.01 IU/ml), while 19% lacked immunity (less than 0.01 IU/ml). After 40 years of age, only 15% showed protective levels. No difference between males and females was seen in the younger population, while women had a lower prevalence of immunity than men among the adult population. Thus, more than 70% of the adult women lacked immunity, while the figure for the men was 50%.