Immunogenicity of tetanus-diphtheria toxoids (Td) among Ukrainian adults: Implications for diphtheria control in the newly independent states of the former Soviet Union

After 30 years of control, epidemic diphtheria returned to the Soviet Union in 1990, To develop control strategies, the immunogenicity of the tetanus and diphtheria toxoids (Td) vaccine was assessed. Workers who were 18-67 years old received two Td immunizations separated by 30 days. A neutralization assay determined diphtheria antitoxin (DAT) on enrollment and on days 7, 30, 60, and 425, On enrollment, 43.0% of 488 workers had DAT <0.1 IU/mL, After one dose, 88.5% had DAT greater than or equal to 0.1 IU/mL, after two doses, 92.2% had greater than or equal to 0.1 IU/mL and >90% of participants <30 or greater than or equal to 50 years of age attained greater than or equal to 1.0 IU/mL; however, only 78.4% of those who were 30-39 years old and 51.8% of those who were 40-49 years old achieved greater than or equal to 1.0 IU/mL after two doses. To control the epidemic in Ukraine, one Td dose should be administered to virtually the entire population (persons 30-49 years old require three doses of Td for optimal individual protection and to maximize population immunity).