Differential Immune Responses to Primary Measles-Mumps-Rubella Vaccination in Israeli Children

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Abstract
Measles remains an important cause of morbidity and mortality worldwide, primarily due to problems associated with delivery of the live attenuated vaccine to susceptible populations. In some developed countries, there is concern about the effects of immunization on the immune system. In this study, we analyzed the responses of 12-month-old Bedouin and Jewish children living in Israel to routine measles-mumps-rubella (MMR) vaccination. Seroconversion to measles was 99% in Bedouin and 79% in Jewish children ( P < 0.01), and that to mumps and rubella was 92 to 100% in both groups. Measles neutralizing antibody titers were higher in Bedouin (333 ± 39 mIU/ml) than Jewish (122 ± 60 mIU/ml) children ( P < 0.002). Immunoglobulin G levels were higher in Bedouin than Jewish children ( P = 0.007) and increased after vaccination ( P = 0.0009). Leukocyte ( P < 0.02) and lymphocyte ( P = 0.04) counts were higher and CD4 lymphocyte percentages were lower ( P < 0.001) in Bedouin than Jewish children before and after vaccination. Leukocyte counts and natural killer cell numbers did not change after vaccination, but lytic activity increased in Bedouin children ( P < 0.005). Spontaneous proliferation of cultured peripheral blood mononuclear cells increased with vaccination, but there were no changes in the proliferative responses to phytohemagglutinin or tetanus toxoid. In summary, no adverse effects of MMR vaccination on immune function were detected. However, there were differences in underlying immunologic parameters and in response to the measles component of the vaccine between Bedouin and Jewish children. It is not known whether genetic differences or environmental exposure accounts for these differences.