Introduction: Infants and young children typically have the highest age-related risk of invasive meningococcal disease. The immunogenicity and safety of a single primary dose and a booster of a meningococcal A/C/W/Y tetanus toxoid conjugate vaccine (MenACWY-TT; Nimenrix®) in infants were evaluated.
Methods: In this phase 3b, open-label, single-arm study, healthy 3-month-old infants received a single Nimenrix dose followed by a booster at age 12 months (1 + 1 series). Functional antibodies before and 1 month after each vaccination were evaluated with serum bactericidal antibody assays using rabbit (rSBA) or human (hSBA) complement for each A/C/W/Y serogroup. Primary endpoints were rSBA seroprotection (titers ≥ 1:8) rates and geometric mean titers (GMTs); supportive secondary endpoints included hSBA seroprotection (titers ≥ 1:4) rates and GMTs. Local reactions and systemic events occurring within 7 days, adverse events (AEs), serious AEs, and newly diagnosed chronic medical conditions following vaccination were assessed.
Results: Overall, 147 and 143 participants received the primary and booster Nimenrix doses, respectively. rSBA seroprotection rates across serogroups were 82.3-91.1% at 1 month after the primary dose and increased to 100% at 1 month after the booster. rSBA GMTs were considerably higher after the booster (1299.5‒2714.1) than after the primary dose (54.7‒202.4). In hSBA evaluations performed as supportive to rSBA evaluations, seroprotection rates increased from 38.8 to 95.5% after the primary dose to 100% after the booster, with corresponding GMT increases (8.8‒149.8 to 1208.4‒7299.6). Local reactions and most systemic events were mild to moderate in severity; no new safety concerns were identified.
Conclusion: Nimenrix given at ages 3 and 12 months had a favorable safety profile and elicited protective immune responses and robust anamnestic booster responses across A/C/W/Y serogroups. These results provide important support for this alternative Nimenrix 1 + 1 immunization schedule for infants < 6 months, allowing flexibility in infant meningococcal immunization.
Trial registration: ClinicalTrials.gov, NCT04819113.
Keywords: Immunogenicity; Infants; Invasive meningococcal disease; MenACWY-TT; Nimenrix; Safety; Vaccination schedules; rSBA.
Infants and young children typically have the highest age-related risk of invasive meningococcal disease, a rare but potentially devastating illness. Nimenrix is a vaccine that protects against meningococcal types A, C, W, and Y, which are among the most common causes of invasive meningococcal disease. Currently, for infants 6 weeks to < 6 months of age, Nimenrix is recommended to be administered as 2 initial doses, and then a booster dose at age 12 months (2 + 1 schedule). In this study, healthy infants received Nimenrix at 3 months (primary dose) and 12 months (booster) of age to assess the possible use of an alternative 1 + 1 schedule. Blood samples from vaccinated infants were evaluated for the presence of antibodies able to kill bacteria for types A/C/W/Y at levels that are considered protective. Before vaccination, 0–8% of infants had antibodies at those levels across the A/C/W/Y types. Percentages increased to range from 82 to 91% at 1 month after the primary dose, then decreased before the booster but reached 100% against each A/C/W/Y type at 1 month after the booster. Antibody levels after the booster were considerably higher than those after the primary dose. The Nimenrix 1 + 1 schedule was well tolerated and safe, reactions were mostly mild to moderate in severity, and no safety concerns were identified. Overall, these results provide important support for the Nimenrix 1 + 1 immunization schedule for infants as young as 3 months, allowing flexibility in infant immunization against meningococcal disease.
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