Immunogenicity and safety of booster CYD-TDV dengue vaccine after alternative primary vaccination schedules in healthy individuals aged 9–50 years: a randomised, controlled, phase 2, non-inferiority study

Background Dengue is endemic in many countries throughout the tropics and subtropics, and the disease causes substantial morbidity and health-care burdens in these regions. We previously compared antibody responses after one-dose, two-dose, or three-dose primary regimens with the only approved dengue vaccine CYD-TDV (Dengvaxia; Sanofi Pasteur, Lyon, France) in individuals aged 9 years and older with previous dengue exposure. In this study, we assessed the need for a CYD-TDV booster after these primary vaccination regimens. Methods In this randomised, controlled, phase 2, non-inferiority study, healthy individuals aged 9-50 years recruited from three sites in Colombia and three sites in the Philippines (excluding those with the usual contraindications to vaccinations) were randomly assigned 1:1:1 via a permuted block method with stratification by site and by age group using an independent voice response system to receive, at 6-month intervals, three doses of CYD-TDV (three-dose group), one dose of placebo followed by two doses of CYD-TDV (two-dose group), or two doses of placebo followed by one dose of CYD-TDV (one-dose group). Participants were also randomly assigned (1:1) to receive a CYD-TDV booster at 1 year or 2 years after the last primary dose. Each CYD-TDV dose was 0.5 mL and administered subcutaneously in the deltoid region of the upper arm. The investigators and sponsor, study staff interacting with the investigators, and participants and their parents or legally acceptable representatives were masked to group assignment. Neutralising antibodies were measured by 50% plaque reduction neutralisation testing, and geometric mean titres (GMTs) were calculated. Due to a change in study protocol, only participants who were dengue seropositive at baseline in the Colombian cohort received a booster vaccination. The primary outcome was to show non-inferiority of the booster dose administered at 1 year or 2 years after the two-dose and three-dose primary regimens; non-inferiority was shown if the lower limit of the two-sided adjusted 95% CI of the between-group (day 28 post-booster dose GMT from the three-dose or two-dose group vs day 28 GMT post-dose three of the three-dose primary regimen [three-dose group]) geometric mean ratio (GMR) was higher than 0.5 for each serotype. Non-inferiority of the 1-year or 2-year booster was shown if all four serotypes achieved non-inferiority. Safety was assessed among all participants who received the booster. This trial is registered with ClinicalTrials.gov, NCT02628444, and is closed to accrual. Findings Between May 2 and Sept 16, u2016, we recruited and enrolled 1050 individuals who received either vaccine or placebo. Of the 350, 348, and 352 individuals randomly assigned to three-dose, two-dose, and one-dose groups, respectively, 108,115, and 115 from the Colombian cohort were dengue seropositive at baseline and received a booster; 55 and 53 in the three-dose group received a booster after 1 year and 2 years, respectively, as did 59 and 56 in the two-dose group, and 62 and 53 in the one-dose group. After the three-dose primary schedule, non-inferiority was shown for serotypes 2 (GMR 0.746; 95% CI 0.550-1.010) and 3 (1.040; 0.686-1.570) but not serotypes 1 (0.567; 0.399-0.805) and 4 (0.647; 0.434-0.963) for the 1-year booster, and again for serotypes 2 (0.871; 0.673-1.130) and 3 (1.150; 0.887-1.490) but not serotypes 1 (0.688; 0.479-0-989) and 4 (0.655; 0.471-0.911) for the 2-year booster. Similarly, after the two-dose primary schedule, non-inferiority was shown for serotypes 2 (0.809; 0.505-1.300) and 3 (1.19; 0.732-1.940) but not serotypes 1(0.627; 0.342-1-150) and 4 (0.499; 0.331-0-754) for the 1-year booster, and for serotype 3 (0.911; 0.573-1-450) but not serotypes 1(0.889; 0.462-1.710), 2 (0.677; 0.402-1-140), and 4 (0.702; 0.447-1-100) for the 2-year booster. Thus, non-inferiority of the 1-year or 2-year booster was not shown after the three-dose or two-dose primary vaccination regimen in dengue-seropositive participants. No safety concerns occurred with the 1-year or 2-year CYD-TDV booster. Interpretation CYD-TDV booster 1 year or 2 years after the two-dose or three-dose primary vaccination regimen does not elicit a consistent, meaningful booster effect against all dengue serotypes in participants who are seropositive for dengue at baseline. Copyright (C) 2022 Elsevier Ltd. All rights reserved.