Immune response to diphtheria booster vaccine in the Baltic states

A study was done to measure baseline levels of immunity to diphtheria and antibody responses to different doses of diphtheria vaccine in study participants in the three Baltic states. Diphtheria booster vaccines containing either 3 (Estonia and Lithuania), 6 (Latvia), or 12 (Latvia) limit of flocculation units of diphtheria toxoid were administered to 2315 adults. Diphtheria antibody levels were tested before and 1-2 months after vaccination. Before vaccination, 40% of the participants in Estonia, 32% in Lithuania, and 38% in Latvia had antibody levels <0.01 IU/mL, the level for minimum protection. After vaccination, 79% of the participants in Estonia, 83% in Lithuania, and 81% in Latvia had antibody levels >0. 1 IU/mL, the minimum level for full protection. However, in each of the countries, about one-third of the 40- to 49-year-old participants would have benefited from additional doses of vaccine. There was not a significantly different antibody response among persons receiving the three different doses. Age and the level of prevaccination immunity had a modifying effect on the response to vaccination; however, sex did not.