Karen McCarthy

Chimeric Live, Attenuated Vaccine against Japanese Encephalitis (ChimeriVax-JE): Phase 2 Clinical Trials for Safety and Immunogenicity, Effect of Vaccine Dose and Schedule, and Memory Response to Challenge with Inactivated Japanese Encephalitis Antigen

ChimeriVax-JE is a live, attenuated vaccine against Japanese encephalitis, using yellow fever (YF) 17D vaccine as a vector. In a double-blind phase 2 trial, 99 adults received vaccine, placebo, or YF 17D vaccine (YF-VAX). ChimeriVax-JE was well tolerated, with no differences in adverse events between treatment groups. Viremias resulting from administration of ChimeriVax-JE and YF-VAX were of short duration and low titer; 82 (94%) of 87 subjects administered graded doses (1.8-5.8 log(10)) of ChimeriVax-JE developed neutralizing antibodies. A second dose, administered 30 days later, had no booster effect. Previous inoculation with YF did not interfere with ChimeriVax-JE, but there was a suggestion (not statistically significant) that ChimeriVax-JE interfered with YF-VAX administered 30 days later. A separate study explored immunological memory both in subjects who had received ChimeriVax-JE 9 months before and in ChimeriVax-JE-naive subjects challenged with inactivated mouse-brain vaccine (JE-VAX). Anamnestic responses were observed in preimmune individuals. ChimeriVax-JE appears to be a safe vaccine that provides protective levels of neutralizing antibody after a single dose.

Clinical proof of principle for ChimeriVax™: recombinant live, attenuated vaccines against flavivirus infections

ChimeriVax is a live, attenuated recombinant virus constructed from yellow fever (YF) 17D in which the envelope protein genes of YF 17D are replaced with the corresponding genes of another flavivirus. A ChimeriVax vaccine was developed against Japanese encephalitis (JE). A randomized, double-blind, outpatient study was conducted to compare the safety and immunogenicity of ChimeriVax-JE and YF 17D. Six YF immune and six non-immune adults were randomized to receive a single SC inoculation of ChimeriVax-JE (5log(10)PFU), ChimeriVax-JE (4log(10)PFU) or YF-VAX((R)) (5log(10)PFU). Mild, transient injection site reactions and flu-like symptoms were noted in all treatment groups, with no significant difference between the groups. Nearly all subjects inoculated with ChimeriVax-JE at both dose levels developed a transient, low-level viremia which was similar in magnitude and duration to that following YF-VAX). Neutralizing antibody seroconversion rates to ChimeriVax-JE was 100% in the high and low dose groups in both naïve and YF immune subjects; seroconversion to wild-type JE strains was similar or lower than to the homologous (vaccine) virus. Mean neutralizing antibody responses were higher in the ChimeriVax-JE high dose groups (naïve subjects LNI 1.55, PRNT(50) 254; YF immune subjects LNI 2.23, PRNT(50) 327) than in the low dose groups (naïve subjects 1.38, PRNT(50) 128; YF immune subjects LNI 1.62, PRNT(50) 270). JE antibody levels were higher in YF immune than in naïve subjects, dispelling concerns about anti-vector immunity. The safety and immunogenicity profile of ChimeriVax-JE vaccine appears to be similar to that of YF 17D. The new vaccine holds promise for prevention of JE in travelers and residents of endemic countries. The ChimeriVax technology platform is being exploited for development of new vaccines against dengue and West Nile.

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.

Yellow Fever 17D Vaccine Safety and Immunogenicity in the Elderly

The incidence of serious and severe multisystem adverse events (AEs) following yellow fever (YF) 17D vaccine is higher in persons of advanced age. One hypothesis for the occurrence of these AEs in the elderly is immunological senescence and a reduced ability to clear the vaccine virus infection. We determined age-specific rates of serious and nonserious AEs in two large clinical trials of two YF 17D vaccines from different manufacturers. In addition, we analyzed AEs reported in a large general practice data base in the United Kingdom. Neutralizing antibody responses were compared in young and elderly subjects. In the clinical trials, involving a total of 4,532 subjects, there were no neurological and viscerotropic AEs; interestingly, the incidence of common injection site and systemic AEs was significantly lower in elderly than in younger subjects. The neutralizing antibody categorical and quantitative responses were equivalent across younger and elderly subjects. In contrast, the larger retrospective analysis of 43,555 persons receiving YF 17D in the UK general practice database revealed a higher incidence of significant neurologic and multisystem AEs with advancing age. The age-specific reporting rate ratio (RRR) was approximately twice that in the 25-44 year-old reference group for subjects in the 45-64 year age group (RRR 1.82; 95% CI 0.88,3.77) and 3-fold higher for the 65-74 year-old age group (RRR 2.82; 95% CI 0.81, 9.81). These results are consistent with previous reports on YF vaccine safety in the US (Martin M, et al. Emerg Infect Dis 2001;6:945-951; Khromova et al., Vaccine 2005;23:3256-3263). In elderly persons, YF 17D vaccine is associated with a higher frequency of significant AEs in the elderly but a lower incidence of common non-serious side-effects. The neutralizing antibody response, which is the mediator of protective immunity to YF, is not diminished in healthy, elderly persons.

Immunogenicity, safety and tolerability in adults of a new single-dose, live-attenuated vaccine against Japanese encephalitis: Randomised controlled phase 3 trials.

Japanese encephalitis chimeric virus vaccine (JE-CV) was developed to replace licensed mouse brain-derived vaccine (MBD-JE), the production of which ceased in 2005. Two randomised controlled phase 3 studies were conducted. Immunogenicity study: 410 participants received one JE-CV injection, 410 received 3 MBD-JE injections. Safety study: 1,601 participants received JE-CV, 403 received placebo. Seroconversion after a single JE-CV vaccination (99.1%) was statistically non-inferior to that after three-dose MBD-JE (95.1%) vaccination. JE-CV elicited a rapid immune response, with 93.6% of participants seroconverting within 14 days. Adverse reaction rates were significantly lower with JE-CV (67.6%) than with MBD-JE (82.2%) (p<0.001), and the reactogenicity profile of JE-CV was comparable with that of placebo. A single dose of JE-CV elicited rapid seroconversion in a higher proportion of vaccinees than the current vaccine with fewer reactions. The safety profile of JE-CV is good.

Long term immunity to live attenuated Japanese encephalitis chimeric virus vaccine: randomized, double-blind, 5-year phase II study in healthy adults.

In a randomized, double-blind study, 202 healthy adults were randomized to receive a live, attenuated Japanese encephalitis chimeric virus vaccine (JE-CV) and placebo 28 days apart in a cross-over design. A subgroup of 98 volunteers received a JE-CV booster at month 6. Safety, immunogenicity, and persistence of antibodies to month 60 were evaluated. There were no unexpected adverse events (AEs) and the incidence of AEs between JE-CV and placebo were similar. There were three serious adverse events (SAE) and no deaths. A moderately severe case of acute viral illness commencing 39 days after placebo administration was the only SAE considered possibly related to immunization. 99% of vaccine recipients achieved a seroprotective antibody titer ≥ 10 to JE-CV 28 days following the single dose of JE-CV, and 97% were seroprotected at month 6. Kaplan Meier analysis showed that after a single dose of JE-CV, 87% of the participants who were seroprotected at month 6 were still protected at month 60. This rate was 96% among those who received a booster immunization at month 6. 95% of subjects developed a neutralizing titer ≥ 10 against at least three of the four strains of a panel of wild-type Japanese encephalitis virus (JEV) strains on day 28 after immunization. At month 60, that proportion was 65% for participants who received a single dose of JE-CV and 75% for the booster group. These results suggest that JE-CV is safe, well tolerated and that a single dose provides long-lasting immunity to wild-type strains.

Concomitant or sequential administration of live attenuated japanese encephalitis chimeric virus vaccine and yellow fever 17D vaccine: Randomized double-blind phase II evaluation of safety and immunogenicity.

A randomized, double-blind, study was conducted to evaluate the safety, tolerability and immunogenicity of a live attenuated Japanese encephalitis chimeric virus vaccine (JE-CV) co-administered with live attenuated yellow fever vaccine (YF-17D strain; Stamaril®, Sanofi Pasteur) or administered successively. Participants (n = 108) were randomized to receive: YF followed by JE-CV 30 days later, JE followed by YF 30 days later, or the co-administration of JE and YF followed or preceded by placebo 30 days later or earlier. Placebo was used in a double-dummy fashion to ensure masking. Neutralizing antibody titers against JE-CV, YF-17D and selected wild-type JE strains was determined using a 50% serum-dilution plaque reduction neutralization test. Seroconversion was defined as the appearance of a neutralizing antibody titer above the assay cut-off post-immunization when not present pre-injection at day 0, or a least a four-fold rise in neutralizing antibody titer measured before the pre-injection day 0 and later post vaccination samples. There were no serious adverse events. Most adverse events (AEs) after JE vaccination were mild to moderate in intensity, and similar to those reported following YF vaccination. Seroconversion to JE-CV was 100% and 91% in the JE/YF and YF/JE sequential vaccination groups, respectively, compared with 96% in the co-administration group. All participants seroconverted to YF vaccine and retained neutralizing titers above the assay cut-off at month six. Neutralizing antibodies against JE vaccine were detected in 82-100% of participants at month six. These results suggest that both vaccines may be successfully co-administered simultaneously or 30 days apart.

Exercise-Induced Serum Enzyme Elevations Confounding the Evaluation of Investigational Drug Toxicity: Report of Two Cases in a Vaccine Trial

Two subjects developed marked elevations in creatine kinase and other serum enzymesassociated with mild myalgia during a randomized, double-blind, controlled Phase 1 clinical trial ofan investigational live, attenuated vaccine against West Nile virus (ChimeriVax™-WN02). Onesubject had received ChimeriVax™-WN02 while the other subject was enrolled in an activecontrol group and received licensed yellow fever 17D vaccine (YF-VAX®). Subsequently, theclinical trial was interrupted, and an investigation was begun to evaluate the enzymeabnormalities. As daily serum samples were collected for determination of quantitative viremia, itwas possible to define the enzyme elevations with precision, and to relate these elevations tophysical activity of the subjects, symptoms, and virological and serological measurements.Evaluation of both subjects clearly showed that skeletal muscle injury, and not cardiac or hepaticdysfunction, was responsible for the biochemical abnormalities. This investigation also implicatedstrenuous exercise as the cause of the apparent muscle injury rather than the study vaccines. Asa result of this experience, subjects engaged in future early-stage trials of these live, attenuatedviral vaccines will be advised not to engage in contact sports or new or enhanced exerciseregimens for which they are not trained or conditioned. The inclusion of placebo control arm (inlieu of or addition to an active vaccine control) will also be useful in differentiating causally relatedserum enzyme elevations.