Background: Immunization of young children against cytomegalovirus (CMV) might decrease child-to-child and child-to-adult transmission of CMV and thereby reduce maternal infection during pregnancy. We conducted a Phase I trial in CMV-seronegative toddlers to evaluate the reactogenicity and immunogenicity of a CMV gB vaccine administered with MF59, an oil and water adjuvant.
Methods: Eighteen children between 12 and 35 months of age received either 20 microg of CMV gB/MF59 (n = 15) or a control hepatitis A vaccine (n = 3) at 0, 1 and 6 months. The study was open-label for the first six children and then observer-blinded and randomized. Children were monitored for local and systemic reactions and for the development of antibodies to the envelope protein gB and CMV-neutralizing antibodies.
Results: Adverse reactions were uncommon and mild. Two children were excluded from the immunogenicity analysis because they had serologic evidence of CMV infection. Reciprocal geometric mean neutralizing titers were: 0 preimmunization (n = 18); 90 (range, 53 to 188) after Dose 2 (n = 6); and 638 (range, 210 to 1645) 1 month after Dose 3 (n = 13). The reciprocal geometric mean neutralizing titers of antibody to gB by EIA were: 0 preimmunization (n = 18); 857 (range, 307 to 2073) after Dose 1 (n = 12); 27 457 (range, 9312 to 55,080) after Dose 2 (n = 6); and 98,264 (range, 35,480 to 228,780) 1 month after Dose 3 (n = 5). After Dose 3 antibody responses of toddlers were greater than those of naturally infected adults and were notably higher than among 149 adults given 3 doses of the same vaccine in other trials.
Conclusion: The CMV gB vaccine is well-tolerated and highly immunogenic in toddlers.