Excessive Attenuation of Measles Virus as a Possible Cause of Failure in Measles Immunization

Summary In order to evaluate the effectiveness of 3 further attenuated measles vaccines, i.e. AIK-HDC, heat-treated AIK-HDC andEdmonston-Zagreb-HDC, they were injected into 743 seronegative children aged 7–72 months. Statistically significant reductions in the seroconversion rates were recorded for heat-treated AIK-HDC as well as for Edmonston-Zagreb-HDC vaccine. Seroconversion rates in all 3 groups of vaccinees were lower for children 7–11 months old. The difference in immunogenicity is attributed to the lower antigenicity of measles viruses treated by heat or successive passages.