Immunogenicity of a Recombinant Human Cytomegalovirus (CMV) gB Vaccine in Toddlers • 745

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Background: Effective immunization of young children against CMV may decrease transmission from children to adults and prevent severe sequelae including congenital birth defects. Objective: To evaluate the reactogenicity and immunogenicity of CHIRON CMV gB vaccine in toddlers. Methods: We conducted a Phase I trial in which 18 CMV-seronegative children, 12-35 months of age, received either 20μg of CMV gB/MF59 vaccine, a purified recombinant gB protein produced in Chinese hamster ovary cell culture combined with MF59, oil and water adjuvant, (n=15) or a control Hepatitis A vaccine from SmithKline Beecham (n=3) at 0,1, and 6 months. The study was open-label for the first 6 children, and then double-blinded and randomized. Children were monitored for local and systemic reactions for 7 days following each injection. Serologic tests for CMV anti-gB antibody by ELISA and CMV neutralizing antibodies were obtained pre-immunization, 1 month after dose 2 in 50% of subjects, and 1 month after.dose 3 in all subjects. Results: No pattern of reactogenicity was observed; 5 post-immunization reactions were seen in 4 subjects. The GMTs (95% CI) of antibody to gB by ELISA were: 0 pre-immunization (n=18), 27,457 (13,794-54,653) after dose 2 (n=6), and 98,264(39,896-242,025) after dose 3 (n=5). Neutralizing antibody reciprocal GMTs(95% CI) were: 0 pre-immunization (n=18), 90 (51-158) after dose 2 (n=6), and 638 (415-982) after dose 3 (n=13). After dose 3, all children had titers greater than those observed in naturally infected adults.Conclusion: Antibody responses of toddlers were notably higher than among 149 adults given 3 doses of the same vaccine in other trials(neutralization GMT=133). CHIRON CMV gB vaccine is well tolerated and highly immunogenic in toddlers.Supported by Chiron Vaccines, Emeryville, CA

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(Spon by: Larry K. Pickering, M.D.)

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