Figure 5. Relationship between the age distributions of infants hospitalized for dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) and the protective and infection-enhancing effects of maternal dengue antibodies. Shown are mean age specific hospitalization rate/1,000 for Bangkok and Thonburi, 1962–1964 (see Figure 1). At birth, antibodies are at protective concentrations. With the passage of time, maternal immunoglobulin G antibodies are catabolized to concentrations that result in antibody-dependent enhancement (ADE) of infections. By the end of the first year of life, ADE antibodies are catabolized to concentrations below the ADE threshold, and DHF/DSS cases disappear.