Ukraine, 1992: First assessment of diphtheria vaccine effectiveness duringthe recent resurgence of diphtheria in the former Soviet Union

A case-control study in Ukraine provided the first data on the field effect iveness of Russian-produced vaccine during the 1990 diphtheria resurgence i n the former Soviet Union. For each of 262 diphtheria cases <15 years of ag e who were reported from January through October 1992, 2 controls, matched by age and clinic, were selected, The effectiveness of three doses of dipht heria vaccine was 98.2% (95%;, confidence interval: 90.3-99.9). Among contr ols, 84% had received three or more vaccinations by 2 years of age. These r esults suggest that the following five hypothesized causes of the outbreak appeared unlikely: appearance of a new "mutant" diphtheria strain, low pote ncy of the Russian-produced diphtheria vaccine, inadequate cold chain, poor host immunogenicity due to radiation exposure from Chernobyl, and low rout ine childhood vaccination coverage. It is concluded that initial priority f or scarce resources for controlling this outbreak should be placed on vacci nation of persons susceptible to diphtheria (e.g., adults) rather than reva ccination of children.