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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, 2016, 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.Funding: Sanofi Pasteur.Translation: For the Spanish translation of the abstract see Supplementary Materials section. [ABSTRACT FROM AUTHOR]

Background: Three doses of the licensed tetravalent dengue vaccine CYD-TDV (Dengvaxia, Sanofi Pasteur, Lyon France) are immunogenic and effective against symptomatic dengue in individuals aged 9 years and older who are dengue seropositive. Previous trials have provided some evidence that antibody responses elicited after just one dose or two doses of CYD-TDV might be similar to those elicited after three doses. We compared antibody responses following one-dose, two-dose, and three-dose vaccination regimens in individuals who were dengue seropositive at baseline up to 1 year after the last injection.Methods: In this randomised, controlled, phase 2, non-inferiority study (CYD65), healthy individuals aged 9-50 years were recruited from the community in three sites in Colombia and three sites in the Philippines. Participants were randomly assigned (1:1:1), using a permuted block method with stratification by site and age group, to receive, at 6-month intervals (on day 0, month 6, and month 12), three doses of CYD-TDV (three-dose group), one dose of placebo (on day 0) and two doses of CYD-TDV (at months 6 and 12; two-dose group), or two doses of placebo (on day 0 and month 6) and one dose of CYD-TDV (at month 12; one-dose group). Each dose of CYD-TDV was 0·5 mL, administered subcutaneously into the deltoid of the upper arm. Participants, study staff, investigators, and the funder were masked to group assignment. The co-primary endpoints were geometric mean titres (GMTs) of neutralising antibodies against each dengue virus serotype at 28 days and 1 year after the last vaccine injection. After a protocol amendment during the conduct of the study, the original co-primary objectives of non-inferiority of the one-dose and two-dose groups to the three-dose group were altered to include non-inferiority of the two-dose group to the three-dose group only, to be assessed in individuals who were dengue seropositive at baseline. Non-inferiority was shown if the lower limit of the 95% CI for the ratio of GMTs (GMR) at 28 days and 1 year between groups was more than 0·5 for each serotype. The analysis of the coprimary objectives was done in the per-protocol analysis dataset, which included all participants who had been vaccinated, had no protocol deviations, and had a valid serology test result for at least one dengue serotype at 28 days after the third injection. Safety was assessed throughout in all participants who received at least one injection of study drug, regardless of serostatus. This trial is registered with ClinicalTrials.gov, NCT02628444, and is closed to accrual.Findings: Between May 2, 2016, and Sept 16, 2016, we recruited and enrolled 1050 individuals, of whom 1048 received at least one injection and 993 had at least one blood sample taken (full-analysis dataset; 333 in three-dose group, 328 in two-dose group, and 332 in one-dose group). 860 (86·6%) of 993 participants in the full-analysis dataset were dengue seropositive at baseline. Non-inferiority (two dose vs three dose) was shown for each serotype at both 28 days and 1 year among dengue-seropositive participants (number of participants assessed: 272 [two-dose group], 265 [three-dose group] at 28 days; and 190 [two-dose group], 185 [three-dose group] at 1 year). At 28 days after the last injection, neutralising antibody GMTs were 899 (95% CI 752-1075) in the two-dose group versus 822 (700-964) in the three dose group against dengue serotype 1 (GMR 1·09 [95% CI 0·86-1·39]); 869 (754-1002) versus 875 (770-995) against serotype 2 (GMR 0·99 [0·82-1·20]); 599 (524-685) versus 610 (535-694) against serotype 3 (GMR 0·98 [0·82-1·18]); and 510 (453-575) versus 531 (470-601) against serotype 4 (GMR 0·96 [0·81-1·14]). At year 1, GMTs had decreased but remained above baseline for all serotypes: 504 (95% CI 403-630) in the two-dose group versus 490 (398-604) in the three-dose group against serotype 1 (GMR 1·03 [0·76-1·40]); 737 (611-888) versus 821 (704-957) against serotype 2 (GMR 0·90 [0·71-1·14]); 437 (368-519) versus 477 (405-561) against serotype 3 (GMR 0·92 [0·72-1·16]); and 238 (205-277) versus 270 (235-310) against serotype 4 (GMR 0·88 [0·72-1·09]). Reactogenicity profiles were similar across treatment groups. Most unsolicited adverse events after any injection were non-serious and systemic in nature. During the study, 60 serious adverse events were reported in 58 participants (14 in three-dose group, 26 in two-dose group, 18 in one-dose group), mostly infection and infestations or injury, poisoning, and procedural complications. No serious adverse events of special interest or admissions to hospital for dengue occurred. Two deaths occurred, unrelated to study treatment.Interpretation: A two-dose CYD-TDV regimen might be an alternative to the licensed three-dose regimen in individuals who are dengue seropositive at baseline and aged 9 years and older. Vaccination with a reduced number of doses could lead to improved vaccine compliance and coverage, especially in low-resource settings.Funding: Sanofi Pasteur. [ABSTRACT FROM AUTHOR]