Protocol Summary: Clinical efficacy and safety of a novel
tetravalent vaccine for Severe Dengue

December 9, 2015

Wendy Charles, MS

Miriam Estin

IsobelleGaleon, MD, MPH

PuujeeJambal, MPH

  1. Background and setting:

Describe the disease or condition. Include basic epidemiology as appropriate. Describe current treatment(s) or standard of care. Describe the new treatment or intervention that will be evaluated in your study. If relevant, consider the following topics from my previous instructions:

Background on the disease or condition that is being targeted

A global public health problem, dengue is currently the most rapidly spreading mosquito-borne viral disease in the world. The incidence of dengue infections have increased 30-fold in the last 50 years (WHO, 2009). From 2003 to 2013, the reported cases of dengue have increased by a factor of five(WHO, 2009). An estimated 390 million dengue infections occur annually, approximately 75% of which occur in the Southeast Asian and Western Pacific Regions, with case fatality rates ranging from 1-5% (WHO, 2009).

Primary or secondary infections with any of the 4 distinct serotypes of the dengue virus (DEN-1 to -4), a small single-stranded RNA virus that belongs to the genus Flavivirus and the family Flaviviridae, occur through the bites of infected Aedesmosquitoes (mostly Ae. aegypti). Infection with any one of the 4 types of dengue virus results in a wide spectrum of illness ranging from asymptomatic or subclinical disease to severe dengue, which manifests with plasma leakage, hemorrhagic tendencies, and death.

The WHO traditionally classified symptomatic infections as undifferentiated fever, dengue fever (DF), and dengue hemorrhagic fever (DHF). The latter category is further classified into four severity grades, with grades III and IV comprising the dengue shock syndrome (DSS). However, this classification has been recently revised to DF with or without warning signs for the development of severe dengue, and severe dengue itself (WHO, 2009; McArthur, Sztein, & Edelman, 2013). Patients with dengue and without warning signs present with fever plus any two of the relevant symptoms (i.e., nausea/vomiting, rash, aches/ pains, leukopenia, and/or a positive tourniquet test) and can be managed at home. Those diagnosed with warning signs fulfilled the above criteria plus one or more symptoms/signs of abdominal pain/tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy/restlessness, liver enlargement >2 cm, and/or laboratory testing showing increased hematocrit (>20% above patient’s baseline value or with concurrent rapid decrease in platelet count) and need to be managed in a hospital. Patients with severe dengue present with severe plasma leakage (i.e. pulmonary edema), bleeding (i.e., melena), and organ involvement (i.e., impaired consciousness) and require emergency treatment. Although most dengue cases follow a self-limiting non-severe course, a small number of patients progress to severe disease. In the Americas, a DHF case fatality rate of 1.2% was reported between 2007-2009 (WHO, 2009). DHF was only reported in 9 countries prior to 1970 (WHO, 2009). This number has subsequently increased to more than 4-fold and continues to rise.

Summary of previous studies in this area. What is known? What is the broader context for the proposed trial?

Vaccination against the dengue virus is currently being explored to lessen the significant burden of disease on the estimated 2.5 billion people who reside in over 100 endemic countries worldwide (WHO, 2009). Since severe dengue tends to occur among young children due to their apparent inability to effectively compensate for capillary leakage, several studies have been recently conducted in this population.

A recent study (Capeding et al., 2014) demonstrated the clinical efficacy (vaccine efficacy: 60.8%; hospitalization for virologically-confirmed disease: 67.2%) and safety of a tetravalent dengue vaccine among 10,275 healthy children, ages 2-14 years old in 5 Asian Pacific countries.

A subsequent follow-up study (Villar et al., 2015) enrolled 20,869 healthy children, ages 9-16 years old, from 5 Latin American countries similarly demonstrated 60.8%, 80.3%, 95.5%, and 91.7% vaccine efficacy rates for dengue fever infection, hospitalization for virologically-confirmed disease (VCD), and hospitalization for severe VCD after 1 and 3 doses, respectively.

Risk factors

Several risk factors that have been found to directly influence dengue severity include secondary infection, age, ethnicity, and chronic diseases. Although primary dengue virus infection is believed to induce lifelong protective immunity to the infecting serotype, and provide protection from clinical and severe illness within 2-3 months and up to 2 years after infection with a different serotype, respectively, no long-term cross-protective immunity has been demonstrated (WHO, 2009; FlipseSmit, 2015).

After the cross-protective period, the risk of developing more severe dengue rises with a secondary infection with a heterotypic serotype and the time between the primary and the secondary infection. A higher case fatality rate has been observed when infection with the DEN-1 virus was followed by DEN- 2 infection after an interval of 20 years, compared to an interval of four years (WHO, 2009).

Although uncommon, a few severe cases with primary infection have also been reported and primarily occur in infants who were born to dengue-immune mothers. Antibody-dependent enhancement (ADE) is believed to be responsible for severe clinical syndrome that is observed in secondary infections and among primarily infected infants. This results in the binding of non-neutralizing, cross-reactive antibodies acquired from a primary infection, or passively at birth, to the surface of a heterologous infecting virus (WHO, 2009). This facilitates virus entry into Fc-receptor-bearing cells resulting in more infected cells, a higher viral burden, a robust host immune response (i.e., the release of inflammatory cytokines and mediators), capillary leakage and eventually, the characteristic signs and symptoms of severe dengue infections. Once activated, cross-reactive memory T cells also rapidly proliferate, express cytokines, and undergo apoptosis, all of which influences the overall disease severity.

What is the key scientific and clinical question that needs to be addressed?

Given the previously presented facts about dengue vaccines and the severity of secondary infections, we have decided to focus our study on investigating the efficacy of the tetravalent vaccine in preventing severe dengue infections among adults with previous VCD. This focus is also pertinent from a public health viewpoint with consideration of the burden on hospitals during endemic transmission seasons and epidemic outbreaks. We aim to address the following relevant clinical question:

Does the administration of 3 doses of a recombinant, live, and attenuated tetravalent dengue vaccine (CYD-TDW) in a 0-6-12 month schedule, lead to fewer hospitalizations secondary to severe dengue, among healthy adults with at least one previous episode of virologically-confirmed disease (VCD)?

The intended indication for the new approach (treatment, intervention, or new test) including: the disease or condition, the target population, the treatment or intervention, and the desired outcome.

Approach: Vaccine intervention

Disease: Virologically-confirmed severe dengue disease, including Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS)

Target population: Healthy adults who have had at least one episode of virologically-confirmed disease (VCD) in Southeast Asia and the Western Pacific

Intervention: Recombinant, live, and attenuated tetravalent dengue vaccine that will be administered in 3 doses, on a 0-6-12 month schedule

Desired outcome: Fewer confirmed hospitalizations for severe dengue

Summary of indication: Recombinant, live, attenuated tetravalent dengue vaccine intervention for the reduction in severity of dengue fever in healthy adults who have had at least one episode of virologically-confirmed disease in order to reduce the number of hospitalizations for severe dengue.

A description of where the proposed trial fits in the sequence of studies (e.g., the phase of the trial).

This study will be a Phase III study to establish the clinical efficacy of the tetravalent dengue vaccine and superiority over placebo. As additional considerations to justify Phase III status, earlier studies were conducted on the vaccine to establish the dosing and toxicity, and this study involves very large sample size where the study population closely reflects the target population.

Give one or two references that describe the setting, or are similar studies to the one you are proposing.

Capeding MR, Tran NH, Hadinegoro SRS, Ismail HIHJ, Chotpitayasunondh T, Chua MN, Luong CQ, Rusmil K, Wirawan DN, Nallusamy R, Pitisuttithum P, Thisyaforn U, Yoon I, van der Vliet D, Langevin E, Laot T, Hutagalung Y, Frago C, Boaz M, Wartel A, Tornieporth NG, Saville M, Boukenooghe A, and the CYD14 Study Group. Clinical efficacy and safety of a novel tetravalent dengue vaccine in healthy children in Asia: a phase 3, randomised, observer-masked, placebo-controlled trial. Lancet. 2014; 384:1358-1365.

Flipse J, Smit JM. The complexity of a dengue vaccine: a review of the human antibody response. PLoS Neglected Tropical Diseases. 2015; 9(6):1-18.

Hadinegoro SR, Arredondo-García JL, Capeding MR, Deseda C, Chotpitayasunondh T, Dietze R, et al. Efficacy and Long-Term Safety of a Dengue Vaccine in Regions of Endemic Disease. New England Journal of Medicine. 2015;373(13):1195-206.

McArthur MA, Sztein MB, Edelman R. Dengue vaccines: recent developments, ongoing challenges, and current candidates. Expert Review of Vaccines. 2013; 12(8):933-953.

Villar L, Dayan GH, Arredondo-García JL, Rivera DM, Cunha R, Deseda C, Reynales H, Costa MS, Morales-Ramirez JO, Carrasquilla G, Rey LC, Dietze R, Luz K, Rivas E, Montoya MCM, SupelanoMC, Zambrano B, Langevin E, Boaz M, Tornieporth N, Saville M, Noriega F, CYD15 Study Group. New England Journal of Medicine. 2015; 372(2):113-123.

WHO. Dengue guidelines for diagnosis, treatment, prevention, and control. Geneva: World Health Organization; 2009.

  1. Synopsis of proposed study:

(a)Study population: Outline eligibility and exclusion criteria

Inclusion criteria: This study will be conducted among healthy adults who are/have:

●18-45 years old

●Previous virologically-confirmed dengue (VCD)

●Residing in urban areas and cities in the endemic provinces of Southeast Asia and the Western Pacific regions

●Have access to participating study field centers and hospitals for enrollment and follow-up

Exclusion criteria: We will exclude patients with:

●Circulating antibodies to other flaviviruses (i.e., Yellow fever) to prevent cross-reactivity

●Previously diagnosed/pre-existing immunocompromised states (i.e., autoimmune diseases, HIV, cancer, diabetes mellitus)

●Identified contraindications to the vaccine and its administration (i.e., with hypersensitivity/adverse drug reactions to the vaccine)

●In the absence of previous studies on the effect of the vaccine on nursing or pregnant mothers, we will also exclude these women from this study.

Case Identification:

Severe cases of dengue will be identified clinically, based on the 2009 WHO criteria, and confirmed by laboratory tests (viral nucleic acid detection by RT-PCR and ELISA). In this study, a case is defined as an episode of symptomatic severe dengue accompanied by evidence of severe plasma leakage, hemorrhage, and organ impairment, which was confirmed virologically by means of enzyme-linked immunosorbent assay for dengue nonstructural protein 1 antigen, dengue screening on quantitative reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assay, or serotype-specific RT-PCR assay. Physicians with specialized training in infectious diseases and who are not involved in the patient’s clinical care will verify cases of severe dengue for inclusion in the analysis.

(b)Study treatment(s): Describe study treatments. Use an appropriate level of detail.

Treatments:

  • Vaccine/Placebo:
  • The tetravalent vaccine consists of four recombinant dengue vaccine viruses (CYD 1 through 4). The strains were be developed by Sanofi Pasteur by substituting genes encoding the proteins of the yellow fever 17D vaccine virus with those from wild-type dengue viruses. Vaccine formulations were combined into a single preparation containing 5.0 log10 median cell-culture infectious doses (CCID50) per serotype and were formulated as a powder and solvent (0.4% sodium chloride) for suspension (Villar, et. al., 2015).
  • Placebo involves a 0.9% solution of sodium chloride.
  • Injection: The vaccine or placebo injections will be administered subcutaneously above the deltoid.

Dosing: Either dengue vaccine or placebo will be administered in 3 doses, on a 0-6-12 month schedule

(c)Study measurements: Define and describe the study measurements that are part of the study. Usually there is a verbal description of each measurement and the measurement method accompanied by a “visit table” showing the visit schedule and measurements made at each visit.

The following measurements will be collected to confirm baseline status and assess for severe dengue disease over the course of study participation.Refer to the Visit Table provided in Figure 1.

Blood samples:

Blood samples will be collected up to three times during study participation to test for dengue non-structural protein 1 antigen (Capeding, et. al, 2014). If the test is positive, subjects will be classified as having virologically-confirmed disease.

  1. As part of routine participation, blood samples will be obtained from all subjects at months 0 and 13.
  2. Subjects suspected of reinfection with acute febrile illness will be asked to come to the clinic to provide blood samples for laboratory exams to confirm dengue infection (i.e., complete blood count, RT-PCR, ELISA) and assess the severity of infection (i.e., liver function tests, serum electrolytes, BUN and creatinine, bicarbonate or lactate, etc.). The goal is to obtain the first sample within 5 days of acute symptoms and the second sample 7 – 14 days later.

Telephone/home follow-up:

  1. During the Active Phase (through month 25), subjects will be contacted every week to collect vaccine-related adverse events and to determine the emergence of dengue disease.
  2. During the Hospital Phase (from Year 3 to Year 6), subjects will receive a phone or home visit every 3 months until the end of the entire study period to collect adverse events and to determine the emergence of dengue disease.
  3. Each subject will be asked to immediately contact the study center/coordinator if he/she develops acute high-grade fever of at least 3 days’ duration at any time after study enrollment for possible dengue infection, as well as potential vaccine-related adverse events.

Questionnaire:

At screening, subjects will complete a questionnaire to collect information regarding their previous medical and medication history (including past history of dengue infection).

Medical records:

Subjectswill provide study coordinators with access to their medical records for post-vaccination hospitalization due to severe dengue within the study period. Medical records will be reviewed:

  1. At the time of post-vaccination hospitalization for suspected dengue virus.
  2. At the conclusion of each subject’s participation (due to withdrawal or completion) to determine unreported hospitalizations for severe dengue, to confirm the diagnosis of severe dengue, and to identify potential vaccine-related adverse events.

(d)Statistical design: Describe the general design. Describe the primary, secondary, and exploratory endpoints for the trial. Propose and evaluate the sample size. Briefly describe the statistical analysis plan:

Trial design: describe the type of design (e.g., double-blind placebo-controlled randomized controlled trial).

The main objective of the trial is to determine long-term safety of the dengue vaccine and to verify that vaccination reduces the risk of severe disease (measured by the incidence of hospitalization for DHF/DSS) in adults in whom immunity has not been additionally boosted.

This study will be designed as a randomized (2:1), placebo-controlled, observer-masked, phase III, multi-center, multi-country trial.

Study Timeline:

Active Phase: Vaccine efficiency and safety will be assessed during 25-month surveillance phase (until 13 months after the third dose was administered).

Hospital Phase: Long-term vaccine safety will be assessed in the follow-up period (from year 3 to year 6), using incidence of hospitalization for DHF/DSS.

The overall study timeline will be 6 years as depicted in Figure 1.

Figure 1

Study endpoints: List and describe primary endpoint, key secondary endpoints, and exploratory endpoints. Note that these should also be listed in the “visit table”.

Primary outcomes:

Annual incidence rate of hospitalization for dengue (DHS/DSS) calculated as the number of cases divided by the total number of participants. The relative risk of hospitalization for VCD will be calculated as the ratio of the annual incidence in vaccine group to that in control group, which is expressed as Vaccine Efficacy (1 − RR).

Secondary outcomes:

  1. ICU admission for Severe Dengue
  2. Mortality rates due to Severe Dengue
  3. All-cause mortality

Visit Table:

The duration of each subject’s participation in the trial will be approximately 6 years. As noted earlier, the duration of the ActivePhase for each subject is expected to be 25 months (12 months of surveillance after Dose 3), and the duration of the HospitalPhase for each subject is expected to be 47 months. Each subject is expected to have a total of 11 Visits during the trial as outlined in the Visit Table below:

Visit Table

Visit Number (V) / V01 / V02 / V03 / V04 / V05 / V06 / V07 / V08 / V09 / V10 / V11
Timelines / D0 / D28 / D180 / V03+28d / D365 / V05+28d / Last Vacc. +13 months / Last Vacc. +24 months / Last Vacc. +36 months / Last Vacc. +48 months / Last Vacc. +60 months
Informed Consent / x / Immunogenicity Test (Subset) / Immunogenicity Test (Subset)
Inclusion/Exclusion Criteria / x
Urine Pregnancy Test / x / x / x
Contraindications / x / x
Physical Exam / x
Clinical Exam and Temp / x / x
History of Dengue or YF Infection/Vaccination / x / x / x / x / x
Concomitant therapy / x / x
Randomization / x / x / x
BL (Dengue Ab) / x
Vaccination / Dose 1 / Dose 2 / Dose 3
Memory Aid (MA) / x / x / x / x / x / x / x / x / x
*Detection of Dengue Cases & Hospitalizations / Throughout the entire trial
Serious Adverse Events / Throughout the entire trial

For V08, V09, V10, and V11, all subjects will be contacted by phone/home visit and will be reminded to come to the study center in case of febrile illness or in case of an adverse event. A clinical examination will be conducted at the Investigator’s discretion and the blood sample will be taken for dengue neutralizing Ab.