Immune responses to measles and mumps vaccination of infants at 6, 9, and 12 months

Immunizing infants against measles at the youngest age possible has the pot ential to reduce morbidity and mortality. The ability of infants at 6, 9, o r 12 months to respond to measles and mumps vaccines was evaluated by measu ring T cell proliferation, interferon-gamma production, and neutralizing an tibody titers before and after vaccination. Infants in all age groups had e quivalent cellular immune responses to measles or mumps viruses, with or wi thout passive antibodies when immunized. In contrast, 6-month-old infants w ithout passive antibodies had low geometric mean titers of antibody to meas les or mumps viruses and low seroconversion rates. Geometric mean titers of antibody to measles virus increased if infants were revaccinated at 12 mon ths. Six-month-old infants had limited humoral responses to paramyxovirus v accines, whereas cellular immunity was equivalent to that of older infants. T cell responses can be established by immunization with these live attenu ated virus vaccines during the first year, despite the presence of passive antibodies.