Imojev

Imojev Mechanism of Action

vaccine, japanese encephalitis

Manufacturer:

Sanofi

Distributor:

Zuellig
/
Four Star
Full Prescribing Info
Action
Pharmacology: Pharmacodynamics: Mechanism of Action: The vaccine is a live attenuated virus. Following administration, the virus replicates locally and elicits neutralising antibodies and cell-mediated immune responses that are specific to the Japanese encephalitis (JE) virus. Available results indicate that protection is mainly mediated by neutralising antibodies.
In nonclinical studies, all animals that received a single dose of the vaccine developed specific neutralising antibodies against JE virus and were protected against infection by a virulent JE virus experimental challenge.
Clinical Trials: Immunogenicity: Passive antibody transfer results in a small animal model indicate that protection is mediated by neutralising antibodies and that the threshold for protection is a plaque reduction neutralisation titre of 1:10.
Immunogenicity data in adult populations: A single dose administration of IMOJEV is as immunogenic as a three-dose regimen of an inactivated Japanese encephalitis (JE) comparator vaccine administered in adults 18 years of age and over.
A seroprotective level of antibodies is generally reached 14 days after vaccination.
In a randomised comparative Phase III trial, 410 individuals over 18 years of age received a single dose of not less than 4.0 log PFU/dose of 0.5 mL of IMOJEV and 410 individuals over 18 years of age received a three-dose regimen of 1 mL of an inactivated JE comparator vaccine.
Thirty days after vaccination, the seroprotection rates for the individuals who received IMOJEV were approximately 99% when measured against the homologous virus strain. These results are non-inferior to those observed after the three-dose regimen of the inactivated JE comparator vaccine.
Fourteen days after a single dose of IMOJEV, approximately 93% of the vaccines showed seroprotective levels of neutralising antibodies.
Table 1 shows the seroprotection rates measured against the homologous virus strain, 14 and 30 days after vaccination with a single dose of IMOJEV or a three-dose regimen of the inactivated JE comparator vaccine. (See Table 1.)

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Neutralising antibody levels were also assessed against a panel of wild-type strains belonging to the four main genotypes and originating from different countries. In a Phase II trial, approximately 89% of vaccinees showed neutralising antibody levels above the 1:10 threshold against the tested wild-type strains, 28 days after a single dose administration of IMOJEV.
In a long-term follow-up assessment in a randomised control phase II trial, 97.6% (95% CI, 93.3; 98.8) of individuals showed seroprotective levels six months after a single administration of IMOJEV. The probability of being still seroprotected 60 months after vaccination for those who were seroprotected at six months is 86.8%.
Long-term immunogenicity data up to Month 60 are presented as Kaplan-Meier estimates in Table 2. (See Table 2.)

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No long-term immunogenicity data beyond 5 years after the administration of a single dose of IMOJEV are available.
Immunogenicity data in paediatric populations: Primary Vaccination: Immune response 28 days after a single dose administration of IMOJEV: A seroprotective level of antibodies is generally reached 28 days after vaccination.
A single dose administration of IMOJEV in 2 randomised trials in 1,231 toddlers (12 to 24 months) not previously immunised with a Japanese encephalitis (JE) vaccine showed that approximately 95% of individuals seroconverted and were seroprotected (neutralising antibody level above the threshold of protection) after 28 days.
Table 3 shows the immune response against the homologous virus strain, 28 days after vaccination with a single dose of IMOJEV. (See Table 3.)

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In addition, approximately 96% of a subset of toddlers previously not immunised with a JE vaccine in a Phase II trial seroconverted to three of the four tested JE wild-type strains 28 days after a single dose administration of IMOJEV, and approximately 70% seroconverted to the fourth strain.
A single dose administration of IMOJEV in a randomised comparative Phase III trial in infants and toddlers (9 to 18 months) (N=126) not previously immunised with a JE vaccine showed more than 99% of individuals seroconverted and were seroprotected after 28 days. These results were non-inferior to those observed after the administration of a live attenuated Japanese encephalitis comparator vaccine. (See Table 4.)

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Immune response up to 5 years after a single dose administration of IMOJEV: The persistence of seroprotection was assessed in Phase II and Phase III trials in toddlers.
In the Phase II trial, approximately 59% of toddlers who did not receive any JE vaccine before the single dose administration of IMOJEV were shown to still have seroprotective antibody levels 5 years after the vaccination.
Table 5 shows the immune response up to 5 years after vaccination with a single dose of IMOJEV. (See Table 5.)

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In the phase III trial, approximately 67% of toddlers who did not receive any JE vaccine before the single dose administration of IMOJEV are still seroprotected 5 years after the vaccination. All the toddlers included in this trial with serological data available 28 days after the vaccination were seroprotected at this time point.
Table 6 shows the immune response against the homologous virus strain, up to 5 years after vaccination with a single dose of IMOJEV. (See Table 6.)

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In another Phase III trial in infants and toddlers (9 to 18 months) not previously immunized with a JE vaccine, approximately 88% of individuals were still seroprotected 1 year after the single dose administration of IMOJEV. (See Table 7.)

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Booster: Booster dose of IMOJEV after primary vaccination with IMOJEV: In a Phase III trial, a second dose (booster dose) of IMOJEV was administered in children (36 to 42 months of age) (N=340) 24 months after primary vaccination with IMOJEV. A control group of children (36 to 42 months of age) (N=39) who never received a JE vaccine, received IMOJEV for the first time to characterise the primary response to IMOJEV.
The Geometric Mean Titre (GMT) increased by nearly 6 fold from Day 0 to Day 7 after the administration of IMOJEV in children previously vaccinated. By comparison, the GMT did not increase in the control group, thus demonstrating an amnestic response in the booster group. The GMT increased by nearly 57 fold from Day 0 to Day 28 in the booster group.
100% of children previously vaccinated with IMOJEV showed seroprotective antibody titres 28 days after the administration of the booster dose 24 months after primary vaccination.
Table 8 shows the immune response against the homologous virus strain, 7 and 28 days after administration of a booster dose of IMOJEV. (See Table 8.)

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In a Phase III trial, a second dose (booster dose) of IMOJEV was administered in children (2 to 4 years of age) (N=97) between 12 and 24 months after primary vaccination with IMOJEV.
The GMT increased by nearly 51 fold from Day 0 to Day 28 in the booster group.
100% of children previously vaccinated with IMOJEV showed seroprotective antibody titres 28 days after the administration of the booster dose between 12 and 24 months after primary vaccination. (See Table 9.)

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In the long-term follow-up assessment of the phase III trial, nearly all children (98.2%) who received the booster dose of IMOJEV 24 months after primary vaccination are still seroprotected 4 years after the vaccination.
Table 10 shows the immune response up to 4 years after vaccination with a booster dose of IMOJEV. (See Table 10).

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Booster vaccination with IMOJEV after the administration of an inactivated JE vaccine as a primary immunisation: In a Phase II trial, IMOJEV was administered to children (N=97) (2 to 5 years) 6 to 38 months after a two-dose primary vaccination with an inactivated JE vaccine (mouse brain-derived JE vaccine).
The GMT increased by nearly 59 fold from Day 0 to Day 28.
Approximately 93% of individuals seroconverted and they were all seroprotected (titre above a threshold considered as protective) 28 days after the administration of IMOJEV.
Table 11 shows the immune response 28 days after the administration of a booster dose of IMOJEV after a primary vaccination with an inactivated JE vaccine. (See Table 11.)

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In addition, approximately 99% of children showed seroprotective antibody levels against JE wild-type strains belonging to the four main genotypes, 28 days after the administration of IMOJEV.
In the long-term follow-up assessment of the phase II trial, nearly all children (96.3%) who received the booster dose of IMOJEV 6 to 38 months after the two-dose primary vaccination with the inactivated JE vaccine are still seroprotected 5 years after the vaccination.
Table 12 shows the immune response up to 5 years after the administration of a booster dose of IMOJEV after a primary vaccination with an inactivated JE vaccine. (See Table 12.)

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