| Pharmacotherapeutic group: Encephalitis vaccines. ATC code: J07BA02 Mechanism of action The mechanism of action of Japanese encephalitis (JE) vaccines is not well understood. Studies in animals have shown that the vaccine triggers the immune system to produce antibodies against Japanese encephalitis virus that are most often protective. Challenge studies were performed in mice that were treated with human IXIARO®antisera. These studies showed that almost all mice that had a Plaque Reduction Neutralization Test titre of at least 1:10 were protected from a lethal Japanese encephalitis virus challenge.Clinical studies No prospective efficacy trials have been performed. Immunogenicity of IXIARO®was studied in approximately 2,060 healthy adult subjects included in five randomized, controlled clinical studies and one non controlled trial.Immunogenicity of the vaccine was evaluated in a randomized, active controlled, observer blinded, multicenter Phase 3 clinical trial including 867 healthy male and female subjects given IXIARO®or the US licensed JEV vaccine JE VAX® (on a 0 , 7 and 28 day schedule by subcutaneous injection). The co primary endpoint was seroconversion rate (anti JEV antibody titer 1:10) and geometric mean titers (GMT) at Day 56 as assessed by a Plaque Reduction Neutralization Test (PRNT) for the entire study population.By Day 56, the proportion of subjects who had seroconverted was similar for both treatment groups (96.4% vs. 93.8% for IXIARO®and JE VAX®, respectively). GMT increased by Day 56 to 243.6 for IXIARO®and to 102.0 for JE VAX®, respectively. The immune responses elicited by IXIARO(r) were non inferior to those induced by JE VAX® (Table 1).Table 1: Seroconversion rates and geometric mean titers of IXIARO(r) and JE VAX(r) in the Per Protocol Population. Neutralising antibody titers against JEV was measured against the JEV strain SA14-14-2.Seroconversion rate | Timepoint | IXIARO® N=365 % (n) | JE-VAX® N=370 % (n) | Visit 0 (Screening) | 0 | 0 | Visit 3 (Day 28) | 54 (197) | 86.8 (321) | Visit 4 (Day 56) | 96.4 (352) | 93.8 (347) | Geometric mean titer (by plaque reduction neutralization test) | Timepoint | IXIARO® N=365 GMT (n) | JE-VAX® N=370 GMT (n) | Visit 0 (Screening) | 5.0 (365) | 5.0 (370) | Visit 3 (Day 28) | 17.4 (363) | 76.9 (367) | Visit 4 (Day 56) | 243.6 (361) | 102.0 (364) | The effect of age on the immune response to IXIARO®and JE VAX®was assessed as a secondary endpoint in this active controlled study, comparing subjects over 50 years of age (N=262, mean age 59.8) with those below 50 years of age (N=605, mean age 33.9).There was no significant difference between seroconversion rates of IXIARO®and JE VAX®in subjects aged <50 years compared to those aged 50 years at Day 28 or Day 56 following vaccination. Geometric mean titers were significantly higher at Day 28 in subjects aged <50 years than those aged 50 years in the JE VAX®group (80.9 vs. 45.9, p=0.0236) but there was no significant difference at Day 56 for this treatment group. There were no significant effects of age on geometric mean titer in the group receiving IXIARO®. There was no significant difference between seroconversion rates in subjects aged <50 years compared to those aged 50 years at Day 28 or Day 56 for either treatment group.The 12 months immune response to IXIARO®was assessed in an uncontrolled Phase 3 follow up clinical trial, enrolling subjects who had completed two pivotal studies, and who received at least one dose of IXIARO®. The primary objective was the evaluation of the immune response to IXIARO®24 months after the first vaccination. Secondary objectives were the evaluation of the immune response to IXIARO®6 and 12 months after the first vaccination and to evaluate the safety of IXIARO®during the respective study period. A total of 3,258 healthy male and female subjects were enrolled of which 2,283 subjects had received IXIARO®, 338 subjects had received JE VAX®, and 637 subjects had received placebo in the respective previous study. Long term immunogenicity to IXIARO®was assessed in a subset of 181 subjects (Intent-to-treat (ITT) population). Immunogenicity data covering a period of 12 months after the first vaccination were as follows:Seroconversion rates for anti JEV antibodies and GMT at Months 2, 6 and 12 are summarized in Table 2 for the ITT population. At Month 2, 98.9% of subjects had seroconverted (95% CI: 96.06, 99.70). By Month 12, the percentage of subjects who had seroconverted was 83.4% (95% CI: 77.33, 88.14). GMT at Months 2, 6, and 12 after vaccination with IXIARO®are summarized in Table 2. At Month 2, the GMT was 310.8 (95% CI: 268.76, 359.44) which decreased to 83.5 (95% CI: 70.89, 98.38) at Month 6 and to 41.2 (95% CI: 34.39, 49.33) at Month 12 after vaccination with IXIARO® (Table 2).Table 2: Seroconversion rates (SCR) and geometric mean titers (GMT) at Month 2, 6 and 12 after vaccination with IXIARO® (ITT population)SCR ITT population | GMT ITT population | | | | N=181 % (n) | 95% Confidence Interval | | N=181 | 95% Confidence Interval | Month 2 | Seroconverted Not seroconverted Missing | 98.9 (179) 0.6 (1) 0.6 (1) | [96.1, 99.7] | Month 2 | 310.8 | [268.8, 359.4] | Month 6 | Seroconverted Not seroconverted | 95.0 (172) 5.0 (9) | [90.8, 97.4] | Month 6 | 83.5 | [70.9, 98.4] | Month 12 | Seroconverted Not seroconverted | 83.4 (151) 16.6 (30) | [77.3, 88.1] | Month 12 | 41.2 | [34.4, 49.3] | The observed decline in GMT is as expected and compares well with data from other inactivated JE vaccines.The concomitant use of IXIARO®with inactivated hepatitis A virus (HAV) vaccine (HAVRIX®1440) has been explored in one clinical trial. There was no interference with the immune response to the JE virus and HAV, respectively. Concomitant administration of IXIARO®and inactivated hepatitis A vaccine was shown to be non-inferior to single vaccinations with regard to GMT of anti-JE virus neutralizing antibody and HAV antibody, and for seroconversion rates of both antibody types (Table 3).Table 3: Seroconversion rates and geometric mean titer of anti JEV neutralizing antibody at Day 56 and seroconversion rates and geometric mean titer for HAV antibody at Day 28 in the Per Protocol PopulationSeroconversion rates and geometric mean titer for anti-JEV neutralizing antibody at Day 56 | | % with SCR | GMT | 95% CI | Group C: IXIARO®
+ HAVRIX®
1440 | 100.0 | 202.7 | [153.7, 261.2] | Group A: IXIARO®
+ Placebo | 98.2 | 192.2 | [147.9, 249.8] | Seroconversion rates and geometric mean titer for HAV antibody at Day 28 | | % with SCR | GMT | 95% CI | Group C: IXIARO®
+ HAVRIX®
1440 | 100.0 | 150.0 | [111.7, 202.3] | Group B: HAVRIX®
+ Placebo | 96.2 | 124.0 | [91.4, 168.2] |
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