Jean Lang

Protective efficacy of the recombinant, live-attenuated, CYD tetravalent dengue vaccine in Thai schoolchildren: a randomised, controlled phase 2b trial

BACKGROUND Roughly half the worlds population live in dengue-endemic countries, but no vaccine is licensed. We investigated the efficacy of a recombinant, live, attenuated tetravalent dengue vaccine. METHODS In this observer-masked, randomised, controlled, monocentre, phase 2b, proof-of-concept trial, healthy Thai schoolchildren aged 4-11 years were randomly assigned (2:1) to receive three injections of dengue vaccine or control (rabies vaccine or placebo) at months 0, 6, and 12. Randomisation was by computer-generated permuted blocks of six and participants were assigned with an interactive response system. Participants were actively followed up until month 25. All acute febrile illnesses were investigated. Dengue viraemia was confirmed by serotype-specific RT-PCR and non-structural protein 1 ELISA. The primary objective was to assess protective efficacy against virologically confirmed, symptomatic dengue, irrespective of severity or serotype, occurring 1 month or longer after the third injection (per-protocol analysis). This trial is registered at ClinicalTrials.gov, NCT00842530. FINDINGS 4002 participants were assigned to vaccine (n=2669) or control (n=1333). 3673 were included in the primary analysis (2452 vaccine, 1221 control). 134 cases of virologically confirmed dengue occurred during the study. Efficacy was 30·2% (95% CI -13·4 to 56·6), and differed by serotype. Dengue vaccine was well tolerated, with no safety signals after 2 years of follow-up after the first dose. INTERPRETATION These data show for the first time that a safe vaccine against dengue is possible. Ongoing large-scale phase 3 studies in various epidemiological settings will provide pivotal data for the CYD dengue vaccine candidate. FUNDING Sanofi Pasteur.

From research to phase III: preclinical, industrial and clinical development of the Sanofi Pasteur tetravalent dengue vaccine.

Dengue vaccine development has reached a major milestone with the initiation, in 2010, of the first phase III clinical trial to investigate the Sanofi Pasteur CYD tetravalent dengue vaccine (TDV). The CYD TDV candidate is composed of four recombinant, live, attenuated vaccines (CYD-1-4) based on a yellow fever vaccine 17D (YFV 17D) backbone, each expressing the pre-membrane and envelope genes of one of the four dengue virus serotypes. The vaccine is genetically and phenotypically stable, non-hepatotropic, less neurovirulent than YFV 17D, and does not infect mosquitoes by the oral route. In vitro and in vivo preclinical studies showed that CYD TDV induces controlled stimulation of human dendritic cells, and significant immune responses in monkeys. Scale up and industrialization are being conducted in parallel with preclinical and clinical development to fulfill the needs of phase II/III trials, and to anticipate and facilitate supply and access to vaccine in the countries where the dengue disease burden makes it an urgent public health priority. The vaccine has now been administered to more than 6000 children and adults from dengue endemic and non-endemic areas and no safety concerns have arisen in any of the completed or ongoing trials. A three-dose vaccination regimen induces an immune response against all four serotypes in the large majority of vaccinees. Preexisting flavivirus immunity favors quicker and higher immune responses to CYD TDV, without adversely effecting clinical safety or increasing vaccine viremia. The observed level and nature of the cellular immune responses in humans are consistent with the good safety and immunogenicity profile of the vaccine. Preliminary results of an ongoing, proof-of-concept efficacy and large scale safety study in Thai children are expected by the end of 2012. Here we discuss the different steps and challenges of developing CYD TDV, from research to industrialization, and summarize some of the challenges to the successful introduction of a dengue vaccine into immunization programs.

Preclinical and clinical development of YFV 17D-based chimeric vaccines against dengue, West Nile and Japanese encephalitis viruses

Dengue viruses (DENV), West Nile virus (WNV) and Japanese encephalitis virus (JEV) are major global health and growing medical problems. While a live-attenuated vaccine exists since decades against the prototype flavivirus, yellow fever virus (YFV), there is an urgent need for vaccines against dengue or West Nile diseases, and for improved vaccines against Japanese encephalitis. Live-attenuated chimeric viruses were constructed by replacing the genes coding for Premembrane (prM) and Envelope (E) proteins from YFV 17D vaccine strain with those of heterologous flaviviruses (ChimeriVax technology). This technology has been used to produce vaccine candidates for humans, for construction of a horse vaccine for West Nile fever, and as diagnostic reagents for dengue, Japanese encephalitis, West Nile and St. Louis encephalitis infections. This review focuses on human vaccines and their characterization from the early stages of research through to clinical development. Phenotypic and genetic properties and stability were examined, preclinical evaluation through in vitro or animal models, and clinical testing were carried out. Theoretical environmental concerns linked to the live and genetically modified nature of these vaccines have been carefully addressed. Results of the extensive characterizations are in accordance with the immunogenicity and excellent safety profile of the ChimeriVax-based vaccine candidates, and support their development towards large-scale efficacy trials and registration.

Live Attenuated Chimeric Yellow Fever Dengue Type 2 (ChimeriVax™-DEN2) Vaccine: Phase I Clinical Trial for Safety and Immunogenicity: Effect of Yellow Fever Pre-immunity in Induction of Cross Neutralizing Antibody Responses to All

A randomized double-blind Phase I Trial was conducted to evaluate safety, tolerability, and immunogenicity of a yellow fever (YF)-dengue 2 (DEN2) chimera (ChimeriVax™-DEN2) in comparison to that of YF vaccine (YF-VAX®). Forty-two healthy YF naïve adults randomly received a single dose of either ChimeriVax™-DEN2 (high dose, 5 log plaque forming units [PFU] or low dose, 3 log PFU) or YF-VAXâ by the subcutaneous route (SC). To determine the effect of YF pre-immunity on the ChimeriVaxTM-DEN2 vaccine, 14 subjects previously vaccinated against YF received a high dose of ChimeriVax™-DEN2 as an open-label vaccine. Most adverse events were similar to YF-VAX® and of mild to moderate intensity, with no serious side-effects. One hundred percent and 92.3% of YF naïve subjects inoculated with 5.0 and 3.0 log10 PFU of ChimeriVaxTM-DEN2, respectively, seroconverted to wt DEN2 (strain 16681); 92% of subjects inoculated with YF-VAX® seroconverted to YF 17D virus but none of YF naïve subjects inoculated with ChimeriVax-DEN2 seroconverted to YF 17D virus. Low seroconversion rates to heterologous DEN serotypes 1, 3, and 4 were observed in YF naïve subjects inoculated with either ChimeriVax™-DEN2 or YF-VAX®. In contrast, 100% of YF immune subjects inoculated with ChimeriVax™-DEN2 seroconverted to all 4 DEN serotypes. Surprisingly, levels of neutralizing antibodies to DEN 1, 2, and 3 viruses in YF immune subjects persisted after 1 year. These data demonstrated that 1) the safety and immunogenicity profile of the ChimeriVax™-DEN2 vaccine is consistent with that of YF-VAX®, and 2) pre-immunity to YF virus does not interfere with ChimeriVaxTM-DEN2 immunization, but induces a long lasting and cross neutralizing antibody response to all 4 DEN serotypes. The latter observation can have practical implications toward development of a dengue vaccine.

A Novel Tetravalent Dengue Vaccine Is Well Tolerated and Immunogenic against All 4 Serotypes in Flavivirus-Naive Adults

BACKGROUND. Sanofi Pasteur has developed a tetravalent dengue vaccine (TDV) against the worlds most common arbovirus infection. METHODS. We assessed the safety and immunogenicity of the TDV in healthy adults randomized into 2 groups. Group 1 received 3 TDV injections at months 0, 4, and 12-15; group 2 received saline placebo at month 0 and then 2 TDV injections at months 4 and 12-15. Adverse events were recorded, and biological parameters and viremia levels were measured. Neutralizing antibodies against 4 World Health Organization (WHO) reference strains were measured before and after vaccinations. RESULTS. A total of 33 participants were enrolled in each group. Demographic characteristics were comparable. No vaccine-related serious adverse event was reported. The most common systemic reactions were headache, malaise, and myalgia. Low viremia levels were detected, mainly of serotype 4. Immune response increased with successive vaccine doses. All participants seroconverted against all 4 serotypes after receiving 3 doses at 0, 4, and 12-15-months, and almost all seroconverted after 2 doses given 8-11 months apart. CONCLUSIONS. Sanofi Pasteurs TDV was well tolerated and induced full seroconversion against all WHO reference strain serotypes after 3 doses.

Safety and immunogenicity of a three dose regimen of two tetravalent live-attenuated dengue vaccines in five- to twelve-year-old Thai children.

Objective. The safety and immunogenicity of tetravalent live-attenuated dengue vaccines after a three dose vaccination series were evaluated in Thai children. Method. One hundred three healthy flavivirus-seronegative schoolchildren ages 5 to 12 years were randomized to receive either dengue vaccine containing 3, 2, 1 and 2 log10 of the 50% cell culture infective dose, respectively, of the live-attenuated dengue vaccine serotypes 1, 2, 3 and 4 per dose (F3212; n = 40) or 3, 3, 1 and 3 log10 of the 50% cell culture infective dose (F3313; n = 42) or purified Vero cell rabies vaccine (control group; n = 21) given in a two dose schedule (3 to 5 months apart). A third dose was administered 8 to 12 months after the second dose to 90 subjects. Safety and immunogenicity were evaluated within 28 days after each injection. Results. No serious adverse event related to the vaccines occurred. Most children experienced mild to moderate fever, rash, headache and myalgia occurring within 12 days after Dose 1 and generally lasting 3 days or less. One subject in Group F3212 had a 1-week dengue-like fever. Reactogenicity was minimal after Doses 2 and 3. Transient mild variations in liver enzymes and hematologic indices were noted mainly after Dose 1. After the third dose 89% of the subjects in Group F3212 seroconverted (neutralizing antibody response, ≥10) to all four serotypes, and all children in Group F3313 seroconverted. Conclusion. This study demonstrates a moderate although improvable reactogenicity and high seroconversion rates against the four serotypes of dengue after a three dose schedule of tetravalent live-attenuated dengue vaccine in children.

Live-attenuated, tetravalent dengue vaccine in children, adolescents and adults in a dengue endemic country: Randomized controlled phase I trial in the Philippines

A recombinant live attenuated tetravalent dengue vaccine (TDV) is safe and immunogenic in adults and children in dengue-naïve populations. Data are needed in dengue endemic populations. In a phase I, randomized, controlled, blind-observer study in the Philippines, groups of participants aged 2-5, 6-11, 12-17, and 18-45 years received either three TDV vaccinations at months 0, 3.5, and 12 (TDV-TDV-TDV group) or licensed typhoid vaccination at month 0 and TDV at months 3.5 and 12 (TyVi-TDV-TDV group) and were followed for safety (including biological safety and vaccine virus viremia) and immunogenicity. No serious adverse vaccine related events and no significant trends in biological safety parameters were reported. Injection site pain, headache, malaise, myalgia, fever, and asthenia were reported most frequently, as mild to moderate in most cases and transient. Reactogenicity did not increase with successive vaccinations and was no higher in children than in adults and adolescents. Low levels of vaccinal viremia were detected in both groups after each TDV vaccination. After three TDV vaccinations, the seropositivity rates against serotypes 1-4 were: 91%, 100%, 96%, 100%, respectively, in 2-5 year-olds; 88%, 96% 96%, 92% in 6-11 year-olds; 88%, 83%, 92%, 96% in adolescents; and 100% for all serotypes in adults. A similar response was observed after two doses for the TyVi-TDV-TDV group. The safety profile of TDV in a flavivirus endemic population was consistent with previous reports from flavivirus naïve populations. A vaccine regimen of either three TDV vaccinations administered over a year or two TDV vaccinations given more than 8 months apart resulted in a balanced antibody response to all four dengue serotypes in this flavivirus-exposed population, including children.

Live-attenuated Tetravalent Dengue Vaccine in Dengue-naïve Children, Adolescents, and Adults in Mexico City: Randomized Controlled Phase 1 Trial of Safety and Immunogenicity.

Background: Preliminary results in healthy, young US adults showed that a tetravalent, live-attenuated dengue vaccine (TDV) was safe and immunogenic, but no data are available in children. Methods: In a multicenter, randomized, controlled, observer-blinded study in the city of Mexico, children aged 2 to 5, 6 to 11, and 12 to 17 years (36 children per age group), and adults (n = 18) aged <45 years received the following: 3 injections of TDV at months 0, 3.5, and 12 (TDV-TDV-TDV), or 1 injection of yellow fever vaccine (YF) at month 0, and 2 injections of TDV at months 3.5 and 12 (YF-TDV-TDV). Adverse events and biologic safety (biochemistry and hematology) were documented. Plaque reduction neutralization test (PRNT50) antibody titers against the TDV parental viruses were measured 28 days after vaccination. Seropositivity was defined as antibody titers ≥10 1/dil. Results: No vaccine-related serious adverse events, other significant clinical adverse events, or clinically significant trends in biologic safety were observed. Reactogenicity did not increase with successive TDV injections, and mild-to-moderate injection site pain, headache, myalgia, and malaise were most commonly reported (14%–40% after each vaccination). After 3 TDV vaccinations, the seropositivity rate against each dengue serotype was in the range 77% to 92%, compared with 85% to 94% after completion of the YF-TDV-TDV regimen. Of the 2- to 11-year-old participants, 95% were seropositive against ≥3 serotypes after 3 vaccinations. Conclusions: A 3-dose TDV regimen had a favorable safety profile in children and adults and elicited neutralizing antibody responses against all 4 serotypes. These findings support the continued development of this vaccine.

Development of Sanofi Pasteur tetravalent dengue vaccine.

The sanofi pasteur tetravalent dengue vaccine candidate is composed of 4 recombinant live attenuated vaccines based on a yellow fever vaccine 17D (YFV 17D) backbone, each expressing the prM and envelope genes of one of the four dengue virus serotypes. Pre-clinical studies have demonstrated that the TV dengue vaccine is genetically and phenotypically stable, non-hepatotropic, less neurovirulent than YFV 17D and does not infect mosquitoes by the oral route. In vitro and in vivo preclinical studies also showed that the TV dengue vaccine induced controlled stimulation in human dendritic cells, and significant immune responses in monkeys. TV dengue vaccine reactogenicity, viraemia induction and antibody responses were investigated in three Phase I trials in the USA, the Philippines and Mexico, in a two or three-dose regimen over a 12 month period. Results showed that the majority of adverse events were mild to moderate and transient in nature. Viraemia was transient and low, and was not increased after initial dengue TV administration, even in the case of incomplete responses. Seropositivity [≥ 10 in a PRNT 50 assay] was 100% for all four serotypes in flavivirus-naive adults injected with 3 doses of TV dengue vaccine in the USA. Similarly, seropositivity was 88–100% following three administrations in flavivirus-naive Mexican children aged 2–5 years. Furthermore, the proportion of seropositive subjects increased with each dengue TV injection in the Philippines where baseline flavivirus immunity was high. Responses were also monitored at the cellular level in humans, and their level and nature were in good agreement with the observed safety and the immunogenicity of the vaccine. Finally, the challenges inherent to the development of such TV dengue vaccines will also be discussed in the last part of this review. In conclusion, preclinical and clinical results support the favorable immunogenicity and short-term safety of the dengue TV vaccine. An extensive clinical development program for dengue TV is underway including completion of the enrollment of 4000 4-11 years old children in an efficacy trial in Thailand, in an area of high dengue incidence. Assuming continued successful outcomes, initial submissions to regulatory authorities are envisaged within a 5-year period.

Antibody Persistence Following Preexposure Regimens of Cell-Culture Rabies Vaccines: 10-Year Follow-Up and Proposal for a New Booster Policy

Subjects (n = 312) received either the human diploid cell rabies vaccine (HDCV) or the purified Vero cell rabies vaccine (PVRV) according to either two-injection (days 0 and 28) or three-injection (days 0, 7, and 28) primary regimens. They received a booster injection at 1 year. Rabies antibody levels were measured after the primary series and the booster and then each year for the next 10 years. The results confirm the superior long-term immunogenicity of the three-injection over the two-injection protocol. HDCV and PVRV in three doses were equally immunogenic. A booster injection at 1 year provides long-term seroconversion (titer > or = 0.5 IU/mL). Antibody titers 2 weeks after the 1-year booster allowed prediction of long-term immunity. Good responders, with titers > or = 30 IU/mL, were protected for at least 10 years. An algorithm for differentiation between good responders and poor responders with respect to vaccine booster strategies is proposed.