Search

The recombinant, live, attenuated, tetravalent dengue vaccine CYD-TDV has shown efficacy against all four dengue serotypes. In this exploratory study (CYD59, NCT02827162), we evaluated potential associations of host human leukocyte antigen (HLA) alleles with dengue antibody responses, CYD-TDV vaccine efficacy, and virologically-confirmed dengue (VCD) cases. Children 4-11 years old, who previously completed a phase 2b efficacy study of CYD-TDV in a single center in Thailand, were included in the study. Genotyping of HLA class I and II loci was performed by next-generation sequencing from DNA obtained from 335 saliva samples. Dengue neutralizing antibody titers (NAb) were assessed as a correlate of risk and protection. Regression analyses were used to assess associations between HLA alleles and NAb responses, vaccine efficacy, and dengue outcomes. Month 13 NAb log geometric mean titers (GMTs) were associated with decreased risk of VCD. In the vaccine group, HLA-DRB1*11 was significantly associated with higher NAb log GMT levels (beta: 0.76; p = 0.002, q = 0.13). Additionally, in the absence of vaccination, HLA associations were observed between the presence of DPB1*03:01 and increased NAb log GMT levels (beta: 1.24; p = 0.005, q = 0.17), and between DPB1*05:01 and reduced NAb log GMT levels (beta: -1.1; p = 0.001, q = 0.07). This study suggests associations of HLA alleles with NAb titers in the context of dengue outcomes. This study was registered with clinicaltrials.gov: NCT02827162.

The presence of Zika virus (ZIKV) in Indonesia has been recognized since the 1970s, but its transmission dynamics there have been poorly understood. To understand more fully the geographic distribution and burden of ZIKV infection, we performed retrospective serological tests on specimens collected from asymptomatic children age 5 to 9 years old living at 30 sites in 14 provinces. Of 870 serum samples tested, 9.2% were found to be positive for anti-ZIKV antibodies, as confirmed by plaque reduction neutralization assays. This was the same overall prevalence reported previously for 1- to 4-year-old children collected at the same sites at the same time. Together with geographic differences in seroprevalence between the age groups, these data suggest that, although ZIKV might be endemic in Indonesia, its occurrence has been focal and episodic.

The tetravalent dengue vaccine (CYD-TDV) is approved for use as a 3-dose series for the prevention of dengue in seropositive individuals ≥9 years. A randomized, placebo-controlled, phase II study of a booster dose of CYD-TDV in individuals who completed the 3-dose schedule >5 years previously (NCT02824198), demonstrated that a booster restored neutralizing antibody titers to post-dose 3 levels. We present additional immunogenicity assessments up to 24 months post-booster, and B- and T-cell responses in a participant subset. Participants aged 9–45 years that had received all three doses of CYD-TDV were randomized 3:1 to receive a booster dose of CYD-TDV (n = 89) or placebo (n = 29). Neutralizing antibody levels at Months 1, 6, 12, and 24 post-booster were assessed by plaque reduction neutralization test. In a subset, B-cell responses were assessed by a fluorescent immunospot assay, and T-cells analyzed by flow cytometry at Days 0, 7, 12, Months 1 and 12. We observed an increase of antibody titers Month 1 post-booster, then a gradual decline to Month 24. In the CYD-TDV booster group, an increase in plasmablasts was seen at Day 7 declining by Day 14, an increase in memory B-cells was observed at Day 28 with no persistence at Month 12. CYD-TDV booster recalled a CD8+ T-cell response, dominated by IFN-γ secretion, which decreased 12 months post-booster. This study showed a short-term increase in antibody titers and then gradual decrease following CYD-TDV booster injection >5 years after primary immunization, and the presence of memory B-cells activated following the booster, but with low persistence.

Dengue endemicity varies but comparative, multicountry data are extremely limited. An improved understanding is needed to prioritize prevention, including vaccination, which is currently recommended only under specific epidemiological conditions. We used serological study data from 46 geographical sites in 13 countries to estimate dengue force of infection (FOI, the proportion of children seroconverting per year) under assumptions of either age-constant or age-varying FOI, and the age at which 50% and 80% of children had been infected. After exclusions, 13 661 subjects were included. Estimated constant FOI varied widely, from 1.7% (Singapore) to 24.1% (the Philippines). In the site-level analysis 44 sites (96%) reached 50% seroconversion and 35 sites (75%) reached 80% seroconversion by age 18 years, with significant heterogeneity. These findings confirm that children living in dengue-endemic countries receive intense early dengue exposure, increasing risk of secondary infection, and imply serosurveys at fine spatial resolutions are needed to inform vaccination campaigns., Dengue transmission is intense in endemic countries, exposing children to a high level of infection at a young age. Transmission risk varies within countries placing communities at unequal risk, requiring serosurveys at fine spatial scales to inform future vaccination strategies.

The tetravalent dengue vaccine (CYD-TDV; Dengvaxia®) is administered on a three-dose schedule, 6 months apart in those aged ≥9 years in a number of dengue-endemic countries in Asia and Latin America. In this study, CYD63 (NCT02824198), participants aged 9–45 years at first vaccination, and who had received three doses of CYD-TDV in the CYD28 study more than 5 years previously, were randomized 3:1 to receive a booster CYD-TDV dose (Group 1) or placebo (Group 2). Dengue neutralizing antibody geometric mean titres (PRNT50 GMTs) for each of the four dengue serotypes were assessed in sera collected before and 28 days after booster injections. Non-inferiority of the booster immune response versus that induced after the third dose was demonstrated for each serotype if the lower limit of the two-sided 95% confidence interval (CI) was >0.5 for the GMT ratios (GMTRs) between post-booster CYD-TDV dose and post-dose 3 in Group 1. Overall, 118 participants received CYD-TDV booster or placebo and 116 (98.3%) completed the study; two participants were withdrawn because of noncompliance. GMTs in the booster CYD-TDV group increased across all serotypes post-booster injection by 1.74- (serotype 1) to 3.58-fold (serotype 4). No discernible increases were observed in the placebo group. Non-inferiority was demonstrated for serotypes 1, 3, and 4, but not for serotype 2 (GMTR; 0.603 [95% CI, 0.439– 0.829]). No safety issues were observed. These data show that the CYD-TDV booster given 5 or more years later tended to restore GMTs back to levels observed post-dose 3.

The CYD-TDV vaccine is licensed in multiple endemic countries based on vaccine efficacy (VE) against symptomatic, virologically confirmed dengue demonstrated in two phase 3 trials (CYD14, 2- to 14-year-olds, Asia; CYD15, 9- to 16-year-olds, Latin America). 50% plaque reduction neutralization test (PRNT(50)) titers at baseline and month 13 (post-vaccination) were associated with VE and may enable bridging VE to adults. Two phase 2 trials of CYD-TDV measured baseline and month 13 PRNT(50) titers: CYD22 (9- to 45-year-olds, Vietnam) and CYD47 (18- to 45-year-olds, India). 50% plaque reduction neutralization test distributions were compared between age cohorts, and four versions of an epidemiological bridging method were used to estimate VE against any serotype (dengue virus [DENV]-Any) and against each serotype over 25 months post first vaccination in a hypothetical CYD14 + CYD15 18- to 45-year-old cohort (bridging population 1) and in the actual CYD47 18- to 45-year-old cohort (bridging population 2). Baseline and month 13 geometric mean PRNT(50) titers to each serotype were significantly greater in 18- to 45-year-olds than 9- to 16-year-olds for all comparisons. The four methods estimated VE against DENV-Any at 75.3–86.0% (95% CIs spanning 52.5–100%) for bridging population 1 and 68.4–77.5% (95% CIs spanning 42.3–88.5%) for bridging population 2. The vaccine efficacy against serotype 1, 2, 3, and 4 was estimated at 56.9–76.9%, 68.3–85.8%, 91.4–95.0%, and 93.2–100% (bridging population 1) and 44.5–66.9%, 53.2–69.2%, 79.8–92.0%, and 90.6–95.0% (bridging population 2), respectively; thus, CYD-TDV would likely confer improved efficacy in adults than 9- to 16-year-olds. Using the same methods, we predicted VE against hospitalized DENV-Any over 72 months of follow-up, with estimates 59.1–73.5% (95% CIs spanning 40.9–92.2%) for bridging population 1 and 50.9–65.9% (95% CIs spanning 38.1–82.1%) for bridging population 2.

Dengue is prevalent in the Asia-Pacific region. Participants of two immunogenicity and safety phase II studies conducted in Singapore and Vietnam (NCT0088089 and NCT00875524, respectively) were followed for up to four years after third vaccine dose of a recombinant, live, attenuated, tetravalent dengue vaccine (CYD-TDV). Participants (2–45 years) received three doses of CYD-TDV or control at 0, 6, and 12 months. Dengue plaque reduction neutralization test (PRNT50) antibody titers were measured in both studies. Cytokine-producing antigen-specific CD4+ and CD8+ T-cells were quantified to assess cell-mediated immunity (CMI) in Singapore. Post-hoc analyses were carried out for participants aged

Background CYD-TDV, a live, attenuated, tetravalent dengue vaccine, has been approved for the prevention of symptomatic dengue in previously dengue exposed individuals. This post hoc analysis assessed hospitalized and severe virologically confirmed dengue (VCD) over the complete 6-year follow-up of 3 CYD-TDV efficacy studies (CYD14, CYD15, and CYD23/CYD57). Methods The main outcomes were hazard ratios (HRs) for hospitalized or severe VCD by baseline dengue serostatus, focusing on those who were seropositive, and by age at immunization (, The final completed 6-year follow-up of 3 CYD-TDV randomized trials in Asia and Latin America confirms the influence of age and prior dengue infection on vaccine effect, indicating protection against hospitalized and severe dengue in seropositives ≥6 years old.

A simplified dose regimen of the live, attenuated, tetravalent dengue vaccine (CYD-TDV) could have the potential to facilitate easier implementation of immunization programs against symptomatic virologically-confirmed dengue (VCD) in dengue seropositive individuals aged ≥ 9 years. This post-hoc analysis of two Phase III studies (CYD14 [NCT01373281] and CYD15 [NCT01374516]) in dengue endemic areas assessed the efficacy of CYD-TDV by dengue serostatus between dose 1 and 2 (at Month [M] 6), between dose 2 and 3 (at M12), and from dose 3 to M25. Baseline dengue serostatus (seropositive or seronegative) was determined based on measured dengue neutralizing antibody titers with the 50% plaque reduction neutralization test (PRNT50) or ascertained by logistic regression-based multiple imputation (MI) to predict PRNT50. Vaccine efficacy against symptomatic VCD was assessed by age and baseline dengue serostatus using a case-cohort framework. Dengue neutralizing antibody geometric mean titers (GMTs) were measured with the PRNT50 at 28 days post-dose 2 and 3. Vaccine efficacy estimates in seropositive participants aged ≥ 9 years at post-dose 1, 2, and 3 were 80.5% (95% CI, 66.2, 88.7), 82.0% (95% CI, 70.5, 89.0), and 75.2% (95% CI, 65.9, 81.9), respectively. In seropositive participants aged

The human leukocyte antigen (HLA) genes are highly variable and are known to play an important role in disease outcomes, including infectious diseases. Prior knowledge of HLA polymorphisms in a population usually forms the basis for an effective case-control study design. As a prelude to future disease association analyses, we report HLA class I and II diversity in 334 unrelated donors from a Dengue vaccine efficacy trial conducted in Thailand. Long-range PCR amplification of six HLA loci was performed on DNA extracted from saliva samples. HLA-A, -B, -C, -DPB1, -DQB1 and -DRB1 were genotyped using a next-generation sequencing method presented at the 17th International HLA and Immunogenetics Workshop. In total, we identified 201 HLA alleles, including 35 HLA-A, 57 HLA-B, 28 HLA-C, 24 HLA-DPB1, 21 HLA-DQB1 and 36 HLA-DRB1 alleles. Very common HLA alleles with frequencies greater than 10 percent were A∗11:01:01, A∗33:03:01, A∗24:02:01, B∗46:01:01, C∗07:02:01, C∗01:02:01, C∗08:01:01, DPB1∗05:01:01, DPB1∗13:01:01, DPB1∗04:01:01, DPB1∗02:01:02, DQB1∗03:01:01, DQB1∗05:02:01, DQB1∗03:03:02, DRB1∗12:02:01, DRB1∗09:01:02, and DRB1∗15:02:01. A novel HLA allele, B∗15:450, had a non-synonymous substitution and occurred in more than one donor. Population-based full-length NGS HLA typing is more conclusive and provides a sound foundation for exploring disease association in a given population.

The live-attenuated Japanese encephalitis chimeric virus vaccine JE-CV (IMOJEV®, Sanofi Pasteur) elicits a robust antibody response in children, which wanes over time. Clinical efficacy is based on a correlate of protection against JE infection defined as neutralizing antibody levels equal to or greater than the threshold of 10 (1/dil). Information on the duration of persistence of the JE antibody response above this threshold is needed. We constructed statistical models using 5-year persistence data from a randomised clinical trial (NCT00621764) in children (2–5 years old) primed with inactivated JE vaccine who received a booster dose of JE-CV, and in JE-naïve toddlers (12–24 months) who received a JE-CV single dose primary vaccination. Models were constructed using a Bayesian Monte-Carlo Markov Chain approach and implemented with OpenBugs V3.2.1. Antibody persistence was predicted for up to 10 years following JE-CV vaccination. Findings from a piecewise model with 2 phases (children) and a classic linear model (toddlers) are presented. For children, predicted median antibody titers (77 [2.5th–97.5th percentile range 41–144] 1/dil) remained above the threshold for seroprotection over the 10 years following booster JE-CV vaccination; the predicted median duration of protection was 19.5 years. For toddlers, 10 years after JE-CV primary vaccination median antibody titers were predicted to wane to around the level required for seroprotection (10.8 [5.8–20.1] 1/dil). A booster dose of JE-CV in children is predicted to provide long-term protection against JE. Such data are useful to facilitate decisions on implementation of and recommendations for future vaccination strategies.

CYD-TDV is a live, attenuated, tetravalent dengue vaccine licensed in 21 countries. We undertook a post-hoc analysis of the long-term efficacy of CYD-TDV during the surveillance expansion phase (SEP) of two Phase III studies (CYD14 in the Asia-Pacific region; CYD15 in Latin America). The SEP included approximately Year 5 and the entire Year 6 of follow-up after the first study injection. Vaccine efficacy against symptomatic virologically-confirmed dengue (VCD) was assessed by participant age (any age, ≥9,9, 2-5, and 6-8 years at the time of the first injection) and baseline dengue serostatus using a case-cohort framework. Baseline dengue serostatus was estimated by several methods including logistic regression-based multiple imputation (MI) to predict PRNT

In efficacy trials of a tetravalent dengue vaccine (CYD-TDV), excess hospitalizations for dengue were observed among vaccine recipients 2 to 5 years of age. Precise risk estimates according to observed dengue serostatus could not be ascertained because of the limited numbers of samples collected at baseline. We developed a dengue anti-nonstructural protein 1 (NS1) IgG enzyme-linked immunosorbent assay and used samples from month 13 to infer serostatus for a post hoc analysis of safety and efficacy.In a case-cohort study, we reanalyzed data from three efficacy trials. For the principal analyses, we used baseline serostatus determined on the basis of measured (when baseline values were available) or imputed (when baseline values were missing) titers from a 50% plaque-reduction neutralization test (PRNTAmong dengue-seronegative participants 2 to 16 years of age, the cumulative 5-year incidence of hospitalization for VCD was 3.06% among vaccine recipients and 1.87% among controls, with a hazard ratio (vaccine vs. control) through data cutoff of 1.75 (95% confidence interval [CI], 1.14 to 2.70). Among dengue-seronegative participants 9 to 16 years of age, the cumulative incidence of hospitalization for VCD was 1.57% among vaccine recipients and 1.09% among controls, with a hazard ratio of 1.41 (95% CI, 0.74 to 2.68). Similar trends toward a higher risk among seronegative vaccine recipients than among seronegative controls were also found for severe VCD. Among dengue-seropositive participants 2 to 16 years of age and those 9 to 16 years of age, the cumulative incidence of hospitalization for VCD was 0.75% and 0.38%, respectively, among vaccine recipients and 2.47% and 1.88% among controls, with hazard ratios of 0.32 (95% CI, 0.23 to 0.45) and 0.21 (95% CI, 0.14 to 0.31). The risk of severe VCD was also lower among seropositive vaccine recipients than among seropositive controls.CYD-TDV protected against severe VCD and hospitalization for VCD for 5 years in persons who had exposure to dengue before vaccination, and there was evidence of a higher risk of these outcomes in vaccinated persons who had not been exposed to dengue. (Funded by Sanofi Pasteur; ClinicalTrials.gov numbers, NCT00842530 , NCT01983553 , NCT01373281 , and NCT01374516 .).

Our objective was to describe the risk of hospital admission for virologically confirmed dengue (VCD) and the risk of clinically severe hospitalized VCD occurring up to 4 years after the first dose (years 1 to 4) in three randomized clinical trials comparing tetravalent dengue vaccine with placebo.The relative risks (RR) for hospitalized VCD from first dose to year 4 were estimated by year and age-group in individual and combined studies.Overall, from Year 1 to Year 4, 233 and 228 participants had at least one episode of hospitalized VCD in the vaccinated (n = 22 603) and placebo (n = 11 301) groups, respectively (RR = 0.511, 95% CI 0.42-0.62). Among these, 48 and 47 cases, respectively, were classified as clinically severe. In children aged ≥9 years, 88 and 136 participants had at least one episode of hospitalized VCD in the vaccinated (n = 17 629) and placebo (n = 8821) groups, respectively (RR = 0.324; 95% CI 0.24-0.43). In vaccinated participants aged9 years, particularly in those aged 2-5 years, there were more hospitalized VCD cases compared with the control participants in Year 3 but not in Year 4. The overall RR in those aged9 years for Year 1 to Year 4 was 0.786 (95% CI 0.60-1.03), with a higher protective effect in the 6-8 year olds than in the 2-5 year olds.The overall benefit-risk remained positive in those aged ≥9 years up to year 4, although the protective effect was lower in years 3 and 4 than in years 1 and 2.

This study shows that the immune response elicited by a Japanese encephalitis chimeric virus vaccine (JE-CV) booster in JE-CV–primed children in the Philippines induces long-lasting protection, and further supports the benefit of a booster irrespective of when primary vaccination was administered., We assessed antibody persistence following booster vaccination with a Japanese encephalitis chimeric virus vaccine (JE-CV; IMOJEV) in JE-CV–primed children. In an open phase 3 trial, 349 children in the Philippines, who received JE-CV 2 years previously, received a booster dose. JE neutralizing antibody titers were assessed (50% plaque reduction neutralization test) annually for up to 5 years after booster vaccination. Seroprotection rates (percentage of children with titers ≥10 [1/dil]) and geometric mean titers (GMTs) were, respectively, 98.2% and 161 after 5 years. JE-CV booster induced long-lasting anamnestic immune response in JE-CV–primed children, with high seroprotection rates and GMTs over the accepted threshold for serological protection (10 [1/dil]). Clinical Trials Registration NCT01190228.

This was a randomized, placebo-controlled, Phase I/II study conducted in a Japanese cohort to assess the safety and immunogenicity of Clostridium difficile vaccine (the same formulation as that used in the ongoing global Phase III study). Healthy Japanese adults aged 40–75 years were randomized to receive either C. difficile vaccine (N = 67) or placebo (N = 34) by intramuscular injection on Days 0, 7, and 30. Serum IgG specific for toxins A and B was measured by enzyme-linked immunosorbent assay (ELISA) and in vitro functional activity by toxin neutralizing assay (TNA). The seroconversion rate (percentage of participants with a ≥4-fold rise in antibody levels from baseline) was high for both toxin A (ELISA and TNA) and toxin B (ELISA), approaching 100% for each by Day 60. For toxin B assessed by TNA, however, the response was lower, with the seroconversion rate not rising significantly beyond the value of 42.9% seen on Day 14 (44.4% at Day 60). Although the response in the participants who were seronegative at baseline was slower than that in those who were seropositive, seroconversion was seen in nearly all (100%) subjects by Day 60, with the exception of the response to toxin B evaluated using TNA (16–18% on Days 14–60). The proportion of participants with solicited local reactions, solicited systemic reactions, and vaccine-related unsolicited reactions were 67.6%, 19.1%, and 20.6%, respectively. Most of the adverse reactions were mild to moderate in intensity, occurring within 3 days post-vaccination, and resolving by 3–6 days post-vaccination. There were no withdrawals due to adverse events and no serious adverse events. These data confirm the safety and immunogenicity of C. difficile vaccine in Japanese adults.

Background We assessed replication and excretion of the live attenuated tetravalent dengue vaccine (CYD-TDV) into biological fluids following vaccination in dengue-naive adults in Australia. Methods Vaccinal viremia/shedding was assessed in a subset of participants enrolled in a lot-to-lot consistency study; 95 participants received 3 subcutaneous doses of CYD-TDV from phase 2/3 lots of the vaccine, and 8 received placebo; doses were administered 6 months apart. Quantitative reverse-transcription polymerase chain reaction (qR-PCR) analysis was used to initially detect the yellow fever virus (YFV) core protein gene in the backbone of CYD-TDV in serum, saliva and urine, followed by serotype-specific qRT-PCR analysis of samples positive for YFV by qRT-PCR (lower limit of detection, 5.16 GEq/mL). Results YFV viremia was detected by qRT-PCR in 69.5% of participants (66 of 95) who received CYD-TDV, mainly 6-14 days after injection 1. The serotypes detected were serotype 4 (in 68.2% of participants [45 of 95]), serotype 3 (in 19.7% [13 of 95]), and serotype 1 (in 12.1% [8 of 95]); serotype 2 was not detected. None of the placebo recipients had vaccinal viremia/shedding. No participants had detectable viral shedding into saliva at levels above the lower limit of quantitation. Two participants had low-level viral shedding (serotype 3) in urine (5.47 and 5.77 GEq/mL). None of the participants with viremia or shedding experienced concomitant fever. Conclusions Low-level vaccinal viremia may occur following vaccination with CYD-TDV, but this is not associated with any symptom or adverse event. Clinical trials registration NCT01134263.

Dengue endemicity varies but comparative, multicountry data are extremely limited. An improved understanding is needed to prioritize prevention, including vaccination, which is currently recommended only under specific epidemiological conditions. We used serological study data from 46 geographical sites in 13 countries to estimate dengue force of infection (FOI, the proportion of children seroconverting per year) under assumptions of either age-constant or age-varying FOI, and the age at which 50% and 80% of children had been infected. After exclusions, 13 661 subjects were included. Estimated constant FOI varied widely, from 1.7% (Singapore) to 24.1% (the Philippines). In the site-level analysis 44 sites (96%) reached 50% seroconversion and 35 sites (75%) reached 80% seroconversion by age 18 years, with significant heterogeneity. These findings confirm that children living in dengue-endemic countries receive intense early dengue exposure, increasing risk of secondary infection, and imply serosurveys at fine spatial resolutions are needed to inform vaccination campaigns.

We described and quantified epidemiologic trends in dengue disease burden in 5 Asian countries (Indonesia, Thailand, Malaysia, Philippines, and Vietnam) and identified and estimated outbreaks impact over the last 3 decades. Dengue surveillance data from 1980 to 2010 were retrieved from DengueNet and from World Health Organization sources. Trends in incidence, mortality, and case fatality rate (CFR) were systematically analyzed using annual average percent change (AAPC), and the contribution of epidemic years identified over the observation period was quantified. Over the 30-year period, incidence increased in all countries (AAPC 1980-2010: 6.7% in Thailand, 10.4% in Vietnam, 12.0% in Indonesia, 18.1% in Malaysia, 24.4% in Philippines). Mortality also increased in Indonesia, Malaysia, and Philippines (AAPC: 6.8%, 7.0%, and 29.2%, respectively), but slightly decreased in Thailand and Vietnam (AAPC: −1.3% and −2.5%), and CFR decreased in all countries (AAPC: −4.2% to −8.3%). Epidemic years, despite representing less than a third of the observation period, contributed from 1 to 3 times more cases versus nonepidemic years. Implementation of more sensitive surveillance methods over the study period may have contributed to a reporting or ascertainment bias in some countries. Nonetheless, these data support the urgent need for novel, integrated, or otherwise effective dengue prevention and control tools and approaches.

A single dose of live attenuated Japanese encephalitis chimeric virus vaccine (JE-CV) was shown to be immunogenic and well tolerated when given either as a booster to formalin-inactivated Japanese encephalitis (JE)-vaccine (mouse brain-derived vaccine [MBDV])-primed 2-5-year-olds, or as a primary vaccination to JE-vaccine-naïve 12-24-month-old toddlers in Thailand. A 5-year follow-up assessment of immune response persistence over time was conducted.Four additional visits (at 2, 3, 4, and 5years) for immunologic assessments were added to the original 12-month open-label crossover study, in which 100 healthy children aged 2-5years with a history of two-dose primary vaccination with MBDV (according to the Thai Expanded Program for Immunization schedule), and 200 healthy JE-vaccine-naïve 12-24-month-old toddlers, were randomized 1:1 to receive JE-CV, containing ⩾4 logIn MBDV-primed 2-5-year-olds (n=78), the immune response to the JE-CV vaccine persisted up to at least 5years after vaccination with a single dose of JE-CV, with all (n=78) children seroprotected at the year 5 visit (geometric mean titers [GMT]: 2521/dil). There was no decrease of seroprotection rate over time (100% at 6months post-vaccination and 96.8% (90.3-98.9) at 5yearspost-vaccination). In JE-vaccine-naïve toddlers, a protective immune response persisted up to at least 5years in 58.8% (50.9-66.4) after a single-dose administration of JE-CV (GMT 26.71/dil; sensitivity analysis).A single-dose of JE-CV as a booster following MBDV administration provided long-lasting immunity. In JE-vaccine-naïve toddlers, despite relatively high seroprotection rates persisting over time, a subsequent booster dose is recommended following a JE-CV primary vaccination for long-term protection. This study was registered on www.clinicaltrials.gov (NCT00621764).

This study evaluated the effect of a booster vaccination of a new, live attenuated, Japanese encephalitis chimeric vaccine (JE-CV). Previously this vaccine has been used as a booster 12 months after priming with an inactivated vaccine and at24 months after priming with the same JE-CV. This study evaluates the immunogenicity and safety of the JE-CV given at 12-24 months after JE-CV priming.Phase III, open-label study in the Republic of Korea in which 119 children previously vaccinated with JE-CV at 12-24 months of age received a JE-CV booster at 12-24 months after primary vaccination. JE neutralizing antibody titers were measured using50% plaque reduction neutralization test prebooster and 1 month postbooster vaccination. Seroprotection (SP) was defined as ≥10 (1/dil). Safety was assessed for 28 days postvaccination by parental reports. Serious adverse events were monitored for 6 months postvaccination.Antibody persistence was high prebooster (SP rate 93.5%). There was a strong anamnestic response postbooster vaccination, with an SP rate of 100% and a50-fold increase in geometric mean titer from the prebooster level. Both antibody persistence and the booster response were independent of whether the booster was given at 12-17 or 18-24 months. The safety profile was good and comparable with the primary vaccination; there were no vaccine-related serious adverse events and no deaths.This study confirms the suitability of a JE-CV booster vaccination at 12-24 months after a primary dose of the same vaccine given at 12-24 months of age in children in the Republic of Korea.

JE-CV (IMOJEV®, Sanofi Pasteur, France) is a live attenuated virus vaccine constructed by inserting coding sequences of the prM and E structural proteins of the Japanese encephalitis SA14-14-2 virus into the genome of yellow fever 17D virus. Primary immunization with JE-CV requires a single dose of the vaccine. This article reviews clinical trials of JE-CV in children aged up to 6 years conducted in countries across South-East Asia. Strong and persistent antibody responses were observed after single primary and booster doses, with 97% of children seroprotected up to five years after booster vaccination. Models of long-term antibody persistence predict a median duration of protection of approximately 30 years after a booster dose. The safety and reactogenicity profiles of JE-CV primary and booster doses are comparable to other widely used childhood vaccines.

Background Japanese encephalitis virus (JEV) is a zoonotic, mosquito-borne flavivirus, distributed across Asia. Infections are mostly mild or asymptomatic, but symptoms include neurological disorders, sequelae, and fatalities. Data to inform control strategies are limited due to incomplete case reporting. Methods We used JEV serological data from a multicountry Asian dengue vaccine study in children aged 2–14 years to describe JEV endemicity, measuring antibodies by plaque reduction neutralization test (PRNT50). Results A total 1479 unvaccinated subjects were included. A minimal estimate of pediatric JEV seroprevalence in dengue-naive individuals was 8.1% in Indonesia, 5.8% in Malaysia, 10.8% in the Philippines, and 30.7% in Vietnam, translating to annual infection risks varying from 0.8% (in Malaysia) to 5.2% (in Vietnam). JEV seroprevalence and annual infection estimates were much higher in children with history of dengue infection, indicating cross-neutralization within the JEV PRNT50 assay. Conclusions These data confirm JEV transmission across predominantly urban areas and support a greater emphasis on JEV case finding, diagnosis, and prevention., Japanese encephalitis virus circulation has been demonstrated in urban areas of Indonesia, Malaysia, the Philippines, and Vietnam. Serological data indicate that up to 5% of children are infected annually.

Dengue seroprevalence data in the literature is limited and the available information is difficult to compare between studies because of the varying survey designs and methods used. We assessed dengue seropositivity across 14 countries using data from 15 trials conducted during the development of a tetravalent dengue vaccine between October 2005 and February 2014. Participants’ dengue seropositivity (n=8592) was determined from baseline (before vaccination) serum samples at two centralized laboratories with the plaque reduction neutralization test (PRNT50). Seropositivity rates generally increased with age in endemic settings. Although seropositivity rates varied across geographical areas, between countries, and within countries by region, no major differences were observed for given age groups between the two endemic regions, Latin America and Asia-Pacific. Seropositivity rates were generally stable over time. The proportion of participants who had only experienced primary infection tended to be higher in younger children than adolescents/adults. These results will help inform and guide dengue control strategies in the participating countries.

BACKGROUND A candidate tetravalent dengue vaccine is being assessed in three clinical trials involving more than 35,000 children between the ages of 2 and 16 years in Asian– Pacific and Latin American countries. We report the results of long-term follow-up interim analyses and integrated efficacy analyses. METHODS We are assessing the incidence of hospitalization for virologically confirmed dengue as a surrogate safety end point during follow-up in years 3 to 6 of two phase 3 trials, CYD14 and CYD15, and a phase 2b trial, CYD23/57. We estimated vaccine efficacy using pooled data from the first 25 months of CYD14 and CYD15. RESULTS Follow-up data were available for 10,165 of 10,275 participants (99%) in CYD14 and 19,898 of 20,869 participants (95%) in CYD15. Data were available for 3203 of the 4002 participants (80%) in the CYD23 trial included in CYD57. During year 3 in the CYD14, CYD15, and CYD57 trials combined, hospitalization for virologically confirmed dengue occurred in 65 of 22,177 participants in the vaccine group and 39 of 11,089 participants in the control group. Pooled relative risks of hospitalization for dengue were 0.84 (95% confidence interval [CI], 0.56 to 1.24) among all participants, 1.58 (95% CI, 0.83 to 3.02) among those under the age of 9 years, and 0.50 (95% CI, 0.29 to 0.86) among those 9 years of age or older. During year 3, hospitalization for severe dengue, as defined by the independent data monitoring committee criteria, occurred in 18 of 22,177 participants in the vaccine group and 6 of 11,089 participants in the control group. Pooled rates of efficacy for symptomatic dengue during the first 25 months were 60.3% (95% CI, 55.7 to 64.5) for all participants, 65.6% (95% CI, 60.7 to 69.9) for those 9 years of age or older, and 44.6% (95% CI, 31.6 to 55.0) for those younger than 9 years of age. CONCLUSIONS Although the unexplained higher incidence of hospitalization for dengue in year 3 among children younger than 9 years of age needs to be carefully monitored during long-term follow-up, the risk among children 2 to 16 years of age was lower in the vaccine group than in the control group. (Funded by Sanofi Pasteur; ClinicalTrials .gov numbers, NCT00842530, NCT01983553, NCT01373281, and NCT01374516.)

Background The recombinant yellow fever-17D-dengue virus, live, attenuated, tetravalent dengue vaccine (CYD-TDV) has undergone extensive clinical trials. Here safety and consistency of immunogenicity of phase III manufacturing lots of CYD-TDV were evaluated and compared with a phase II lot and placebo in a dengue-naive population. Methods Healthy 18–60 year-olds were randomly assigned in a 3:3:3:3:1 ratio to receive three subcutaneous doses of either CYD-TDV from any one of three phase III lots or a phase II lot, or placebo, respectively in a 0, 6, 12 month dosing schedule. Neutralising antibody geometric mean titres (PRNT50 GMTs) for each of the four dengue serotypes were compared in sera collected 28 days after the third vaccination—equivalence among lots was demonstrated if the lower and upper limits of the two-sided 95% CIs of the GMT ratio were ≥0.5 and ≤2.0, respectively. Results 712 participants received vaccine or placebo and 614 (86%) completed the study; 17 (2.4%) participants withdrew after adverse events. Equivalence of phase III lots was demonstrated for 11 of 12 pairwise comparisons. One of three comparisons for serotype 2 was not statistically equivalent. GMTs for serotype 2 in phase III lots were close to each other (65.9, 44.1 and 58.1, respectively). Conclusions Phase III lots can be produced in a consistent manner with predictable immune response and acceptable safety profile similar to previously characterised phase II lots. The phase III lots may be considered as not clinically different as statistical equivalence was shown for serotypes 1, 3 and 4 across the phase III lots. For serotype 2, although equivalence was not shown between two lots, the GMTs observed in the phase III lots were consistently higher than those for the phase II lot. As such, in our view, biological equivalence for all serotypes was demonstrated.

Dengue is a mosquito-borne viral disease that is endemic in India. We evaluated the immunogenicity and safety of recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) in Indian adults. In this observer-blind, randomized, placebo-controlled, Phase II study, adults aged 18-45 years were randomized 2:1 to receive CYD-TDV or placebo at 0, 6 and 12 months in sub-cutaneous administration. Immunogenicity was assessed using a 50% plaque reduction neutralization test (PRNT50) at baseline and 28 days after each study injection. 189 participants were enrolled (CYD-TDV [n = 128]; placebo, [n = 61]). At baseline, seropositivity rates for dengue serotypes 1, 2, 3 and 4 ranged from 77.0% to 86.9%. Seropositivity rates for each serotype increased after each CYD-TDV injection with a more pronounced increase after the first injection. In the CYD-TDV group, geometric mean titres (GMTs) were 2.38 to 6.11-fold higher after the third injection compared with baseline but remained similar to baseline in the placebo group. In the CYD-TDV group, the GMTs were 1.66 to 4.95-fold higher and 9.23 to 24.6-fold higher after the third injection compared with baseline in those who were dengue seropositive and dengue seronegative, respectively. Pain was the most commonly reported solicited injection site reaction after the first injection in both the CYD-TDV (6.3%) and placebo groups (4.9%), but occurred less frequently after subsequent injections. No serious adverse events were vaccine-related, no immediate unsolicited adverse events, and no virologically-confirmed cases of dengue, were reported during the study. The immunogenicity and safety of CYD-TDV was satisfactory in both dengue seropositive and seronegative Indian adults.

Background Indonesia reports the second highest dengue disease burden in the world; these data are from passive surveillance reports and are likely to be significant underestimates. Age-stratified seroprevalence data are relatively unbiased indicators of past exposure and allow understanding of transmission dynamics. Methodology/Principal Findings To better understand dengue infection history and associated risk factors in Indonesia, a representative population-based cross-sectional dengue seroprevalence study was conducted in 1–18-year-old urban children. From October to November 2014, 3,210 children were enrolled from 30 geographically dispersed clusters. Serum samples were tested for anti-dengue IgG antibodies by indirect ELISA. A questionnaire investigated associations between dengue serologic status and household socio-demographic and behavioural factors. Overall, 3,194 samples were tested, giving an adjusted national seroprevalence in this urban population of 69.4% [95% CI: 64.4–74.3] (33.8% [95% CI: 26.4–41.2] in the 1–4-year-olds, 65.4% [95% CI: 69.1–71.7] in the 5–9-year-olds, 83.1% [95% CI: 77.1–89.0] in the 10–14-year-olds, and 89.0% [95% CI: 83.9–94.1] in the 15–18-year–olds). The median age of seroconversion estimated through a linear model was 4.8 years. Using a catalytic model and considering a constant force of infection we estimated 13.1% of children experience a primary infection per year. Through a hierarchical logistic multivariate model, the subject’s age group (1–4 vs 5–9 OR = 4.25; 1–4 vs. 10–14 OR = 12.60; and 1–4 vs 15–18 OR = 21.87; p, Author summary Indonesia reported to the WHO the world’s second highest average number of dengue cases and the highest in Asia from 2004 to 2010. These passive surveillance reports vary widely within the country and are likely to be a severe under-estimation of the full disease burden as frequently only dengue haemorrhagic fever is captured. Understanding the intensity of dengue virus transmission and associated risk factors nationwide is necessary to guide and prioritize appropriate prevention and control measures against dengue disease, especially considering the availability of the first dengue vaccine and recent recommendations for its use in areas of high endemicity, as measured by seroprevalence and other indicators. Age-stratified seroprevalence data provide robust estimates of past exposure and can inform on transmission intensity. Therefore, we conducted a seroprevalence study of anti-dengue IgG antibodies in a representative sample of urban-dwelling Indonesian children. We found an overall dengue seroprevalence of 69.4% with half of the children having been infected at least once by the age of 5 years. Age of the subject and the number of dengue cases diagnosed in the household were associated with serostatus. These results confirm the high dengue disease burden in Indonesia and the urgency of implementation of effective prevention and control measures.

Vaccination with the tetravalent dengue vaccine induces bias toward false-positive dengue diagnosis based on immunoglobulin M and immunoglobulin G assessments. This bias will reduce the utility of these serological markers for dengue diagnosis in populations where the vaccine has been introduced., Background We previously reported that vaccination with the tetravalent dengue vaccine (CYD-TDV; Dengvaxia) may bias the diagnosis of dengue based on immunoglobulin M (IgM) and immunoglobulin G (IgG) assessments. Methods We undertook a post hoc pooled analysis of febrile episodes that occurred during the active surveillance phase (the 25 months after the first study injection) of 2 pivotal phase III, placebo-controlled CYD-TDV efficacy studies that involved ≥31000 children aged 2–16 years across 10 countries in Asia and Latin America. Virologically confirmed dengue (VCD) episode was defined with a positive test for dengue nonstructural protein 1 antigen or dengue polymerase chain reaction. Probable dengue episode was serologically defined as (1) IgM-positive acute- or convalescent-phase sample, or (2) IgG-positive acute-phase sample and ≥4-fold IgG increase between acute- and convalescent-phase samples. Results There were 1284 VCD episodes (575 and 709 in the CYD-TDV and placebo groups, respectively) and 17673 other febrile episodes (11668 and 6005, respectively). Compared with VCD, the sensitivity and specificity of probable dengue definition were 93.1% and 77.2%, respectively. Overall positive and negative predictive values were 22.9% and 99.5%, respectively, reflecting the much lower probability of correctly confirming probable dengue in a population including a vaccinated cohort. Vaccination-induced bias toward false-positive diagnosis was more pronounced among individuals seronegative at baseline. Conclusions Caution will be required when interpreting IgM and IgG data obtained during routine surveillance in those vaccinated with CYD-TDV. There is an urgent need for new practical, dengue-specific diagnostic algorithms now that CYD-TDV is approved in a number of dengue-endemic countries. Clinical Trials Registration NCT01373281 and NCT01374516.

Several ChimeriVax-Dengue (CYD)-based vaccination strategies were investigated as potential alternatives to vaccination with tetravalent CYD vaccine (CYD-TDV) in this phase IIa trial conducted in 2008–9 in 150 healthy adults. Participants were randomized and vaccinated on D0 and D105 (± 15 days). One group received bivalent CYD vaccine against serotypes 1 and 3 (CYD-1;3) on day 0 and CYD-2;4 on day 105 (±15 days). Two groups received an injection at each timepoint of a tetravalent blend of CYD-1;3;4 and a VERO cell derived, live attenuated vaccine against serotype 2 (VDV-2), or the reference CYD-TDV. A fourth group received Japanese encephalitis (JE) vaccine on days -14, -7 and 0, followed by CYD-TDV on day 105. Viraemia was infrequent in all groups. CYD-4 viraemia was most frequent after tetravalent vaccination, while CYD-3 viraemia was most frequent after the first bivalent vaccination. Immunogenicity as assessed by 50% plaque reduction neutralisation test on D28 was comparable after the first injection of either tetravalent vaccine, and increased after the second injection, particularly with the blended CYD-1;3;4/ VDV-2 vaccine. In the bivalent vaccine group, immune response against serotype 3 was highest and the second injection elicited a low immune response against CYD 2 and 4. Immune responses after the first injection of CYD-TDV in the JE-primed group were in general higher than after the first injection in the other groups. All tested regimens were well tolerated without marked differences between groups. Bivalent vaccination showed no advantage in terms of immunogenicity. Clinical trial registration number: NCT00740155

Summary Background An estimated 100 million people have symptomatic dengue infection every year. This is the first report of a phase 3 vaccine efficacy trial of a candidate dengue vaccine. We aimed to assess the efficacy of the CYD dengue vaccine against symptomatic, virologically confirmed dengue in children. Methods We did an observer-masked, randomised controlled, multicentre, phase 3 trial in five countries in the Asia-Pacific region. Between June 3, and Dec 1, 2011, healthy children aged 2–14 years were randomly assigned (2:1), by computer-generated permuted blocks of six with an interactive voice or web response system, to receive three injections of a recombinant, live, attenuated, tetravalent dengue vaccine (CYD-TDV), or placebo, at months 0, 6, and 12. Randomisation was stratified by age and site. Participants were followed up until month 25. Trial staff responsible for the preparation and administration of injections were unmasked to group allocation, but were not included in the follow-up of the participants; allocation was concealed from the study sponsor, investigators, and parents and guardians. Our primary objective was to assess protective efficacy against symptomatic, virologically confirmed dengue, irrespective of disease severity or serotype, that took place more than 28 days after the third injection. The primary endpoint was for the lower bound of the 95% CI of vaccine efficacy to be greater than 25%. Analysis was by intention to treat and per procotol. This trial is registered with ClinicalTrials.gov, number NCT01373281. Findings We randomly assigned 10 275 children to receive either vaccine (n=6851) or placebo (n=3424), of whom 6710 (98%) and 3350 (98%), respectively, were included in the primary analysis. 250 cases of virologically confirmed dengue took place more than 28 days after the third injection (117 [47%] in the vaccine group and 133 [53%] in the control group). The primary endpoint was achieved with 56·5% (95% CI 43·8–66·4) efficacy. We recorded 647 serious adverse events (402 [62%] in the vaccine group and 245 [38%] in the control group). 54 (1%) children in the vaccine group and 33 (1%) of those in the control group had serious adverse events that happened within 28 days of vaccination. Serious adverse events were consistent with medical disorders in this age group and were mainly infections and injuries. Interpretation Our findings show that dengue vaccine is efficacious when given as three injections at months 0, 6, and 12 to children aged 2–14 years in endemic areas in Asia, and has a good safety profile. Vaccination could reduce the incidence of symptomatic infection and hospital admission and has the potential to provide an important public health benefit. Funding Sanofi Pasteur.

Background The live, attenuated Japanese encephalitis (JE) chimeric virus vaccine (JE-CV) is licensed in Thailand and Australia for prophylaxis of JE in individuals at the age of 12 months. JE-CV has not yet been compared with the SA14-14-2 JE vaccine, which is also licensed in Thailand. Methods In this phase 3, observer-blinded trial, 300 children at the age of 9-18 months were randomized 1:1 to receive 1 dose of JE-CV or SA14-14-2. JE neutralizing antibody titers were assessed using PRNT50. The primary endpoint was the noninferiority of seroconversion against JE on Day 28 after JE-CV compared with SA14-14-2, as assessed using the 95% confidence interval of the difference between the groups. Safety and reactogenicity were described in each group using conventional methods, including the reporting of solicited and unsolicited adverse events. Results The seroconversion rate on Day 28 was 99.2% in each group. Noninferiority was demonstrated as the difference between the JE-CV and SA14-14-2 groups was -0.012 percentage points (95% confidence interval: -3.6 to 3.6), which was above the required -10%. The seroprotection rate remained very high at Month 6 and comparable between groups, but a slight decrease was observed in the JE-CV group between Months 6 and 12. Current recommendations for both vaccines call for a booster dose 12-24 months after primary immunization to maintain high seroprotection rates in the long term. Geometric mean titers (GMTs) on Day 28 after vaccination were 507 (1/dil) in the JE-CV group and 370 (1/dil) in the SA14-14-2 group, decreasing by 4.3-fold and 3.6-fold, respectively, to Month 6 before remaining stable to Month 12 and comparable between groups. Solicited reactions were all reported at lower rates after vaccination with JE-CV compared with SA14-14-2. Conclusions A single dose of JE-CV elicited a noninferior immune response compared with SA14-14-2 and had a satisfactory safety profile.

BACKGROUND Japanese encephalitis (JE) is an important mosquito-borne viral disease that is endemic in Asia, Western Pacific countries and Northern Australia. Although there is no antiviral treatment, vaccination is effective in preventing this disease. METHODS We followed a cohort of 596 children for 5 years after primary vaccination at 12-18 months of age with JE chimeric virus vaccine (JE-CV; IMOJEV) in a multicenter, phase III trial in Thailand and the Philippines to assess antibody persistence and safety. At the end of the 5 years, a subgroup of 85 participants, at 1 site in Thailand, was followed after administration of a JE-CV booster vaccination. JE antibody titers were measured annually after primary vaccination and 28 days after booster vaccination using a 50% plaque reduction neutralization test. Seroprotection was defined as a JE-CV neutralizing antibody titer ≥10 (1/dil). Kaplan-Meier survival analysis was used to estimate the proportion of participants maintaining protective JE-CV neutralizing antibody titers. RESULTS At 1, 2, 3, 4 and 5 years after vaccination with JE-CV, 88.5%, 82.9%, 78.2%, 74.0% and 68.6% of the participants followed remained seroprotected. Geometric mean titers in the subgroup assessed after receipt of a booster dose increased from 61.2 (95% confidence interval: 43.8-85.7) pre-booster to 4951 (95% confidence interval: 3928-6241) 28 days post-booster, with all participants seroprotected. There were no safety concerns identified. CONCLUSIONS Protective immune responses persisted for at least 5 years after a JE-CV primary immunization in the majority of participants. JE-CV booster induced a robust immune response even after a 5-year interval.

Objective: To investigate the long-term safety of a tetravalent dengue vaccine (CYD-TDV) in children in a phase Π b follow-up study in Thailand. Methods: In the phase Π b study, children aged 4-11 years were randomized (2:1) to receive three injections of CYD-TDV or serve as control at 6-month intervals, with 25 months’ active follow-up (active phase). This study was an additional four-year passive surveillance for hospitalized virologically-confirmed dengue (VCD; hospital phase). Cases of hospitalized VCD, severe hospitalized VCD, vaccine-related serious adverse events, and deaths were reported for the total population, with post-hoc analyses by enrollment age (

To characterize the cell mediated immunity (CMI) induced by the investigational CYD tetravalent dengue vaccine (TDV), we developed a whole-blood, intracellular cytokine staining (ICS) assay and a multiplex assay, each requiring 3 mL of blood. We assessed CMI before and 28 d after a first and third injection of CYD-TDV and one year after the third injection in a subset of 80 adolescents and adults enrolled in a phase II trial in Singapore (ClinicalTrial.gov NCT NCT00880893). CD4/IFNγ/TNFα responses specific to dengue NS3 were detected before vaccination. Vaccination induced YF-17D-NS3-specific CD8/IFNγ responses, without significant TNFα, and a CYD-specific Th1/Tc1 cellular response in all participants, which was characterized by predominant IFNγ secretion compared with TNFα, associated with low level IL-13 secretion in multiplex analysis of peripheral blood mononuclear cells (PBMC) supernatants after restimulation with each the CYD vaccine viruses. Responses were directed mainly against CYD-4 after the first vaccination, and were more balanced against all four serotypes after the third vaccination. The same qualitative profile was observed one year after the third vaccination, with approximately 2-fold lower NS3-specific responses, and 3-fold lower serotype-specific cellular responses. These findings confirm previous observations regarding both the nature and specificity of cellular responses induced by CYD-TDV, and for the first time demonstrate the persistence of cellular responses after one year. We also established the feasibility of analyzing CMI with small blood samples, allowing such analysis to be considered for pediatric trials.

Japanese encephalitis chimeric virus vaccine (JE-CV) is a licensed vaccine indicated in a single dose administration for primary immunization. This controlled phase III comparative trial enrolled children aged 36-42 mo in the Philippines. 345 children who had received one dose of JE-CV in a study two years earlier, received a JE-CV booster dose. 105 JE-vaccine-naïve children in general good health were randomized to receive JE-CV (JE-vaccine naïve group; 46 children) or varicella vaccine (safety control group; 59 children). JE neutralizing antibody titers were assessed using PRNT50. Immunological memory was observed in children who had received the primary dose of JE-CV before. Seven days after the JE-CV booster dose administration, 96.2% and 66.8% of children were seroprotected and had seroconverted, respectively, and the geometric mean titer (GMT) was 231 1/dil. Twenty-eight days after the JE-CV booster dose seroprotection and seroconversion were achieved in 100% and 95.3% of children, respectively, and the GMT was 2,242 1/dil. In contrast, only 15.4% of JE-CV-vaccine naïve children who had not received any prior JE vaccine were seroprotected seven days after they received JE-CV. One year after receiving the JE-CV booster dose, 99.4% of children remained seroprotected. We conclude that JE-CV is effective and safe, both as a single dose and when administrated as a booster dose. A booster dose increases the peak GMT above the peak level reached after primary immunization and the antibody persistence is maintained at least one year after the JE-CV booster dose administration. Five year follow up is ongoing.