Pharmacotherapeutic group: other viral vaccines, ATC code: not yet assigned
Mechanism of action
VIMKUNYA is an adjuvanted VLP recombinant protein vaccine. VLPs cannot infect cells, reproduce, or cause disease. The exact mechanism of protection against CHIKV infection and/or disease has not been determined. It is thought that VIMKUNYA can induce protection from CHIKV infection by inducing neutralising antibodies against the CHIKV proteins C, E1, and E2 contained in VIMKUNYA resulting in neutralisation of live virus. An adjuvant is added to increase the magnitude of vaccine-mediated immune responses.
Immunogenicity
No efficacy data are available for VIMKUNYA. The clinical efficacy was inferred from a postvaccination CHIKV-specific neutralizing antibody titre threshold.
A threshold of anti-CHIKV serum neutralising antibody (SNA) titre ≥ 100, providing 80% neutralisation of CHIKV, as measured by an in vitro neutralizing assay, was selected as surrogate marker likely to predict protection from disease caused by CHIKV, referred to as seroresponse. This threshold was determined on the basis of a prospective sero-epidemiologic study in individuals with prior exposure to CHIKV and a non-human primate (NHP) passive transfer/challenge study using pooled sera from participants vaccinated with VIMKUNYA vaccine.
The immunogenicity of a single 40 micrograms dose of VIMKUNYA was evaluated in two pivotal studies conducted in the US, one phase 3 clinical study in adolescents and adults 12 to < 65 years of age (Study 1), and one phase 3 clinical study in adults ≥ 65 years of age (Study 2). Participants in both phase 3 studies were followed up for 6 months after vaccination. Difference in anti-CHIKV SNA seroresponse rate (VIMKUNYA vaccine minus placebo) and anti-CHIKV SNA geometric mean titre (GMT) at 21 days post-vaccination (study visit day 22) were both co-primary endpoints. The seroresponse rate (SRR) was defined as the percentage of individuals who achieved an anti-CHIKV SNA NT80 titre ≥ 100. Immunocompromised individuals and individuals with prior receipt of immunosuppressive medications from 6 months prior to screening medications were excluded from study participation.
Study 1
This study was a phase 3 pivotal, randomised, multicentre, placebo-controlled, double-blind, parallel-group clinical study conducted in the US. A total of 3 258 healthy participants aged between 12 and < 65 years of age (mean age 39 years of age [range 12 to 64]) were randomised in a 2:2:2:1 ratio within each age stratum (12 to < 18 (N = 254; 7.8%), 18 to < 46 (N=1 906; 58.5%), and 46 to <65 years of age (N = 1 098; 33.7%)) to receive either one of three consecutively manufactured lots of VIMKUNYA as a single intramuscular 40 micrograms dose in a pre-filled syringe, or placebo. In the randomised population, 1 591 (48.8%) were males and 1 667 (51.2%) were females. There were 69 baseline seropositive participants (defined as Day 1 predose anti-CHIKV titre ≥ 15 (≥ assay lower limit of quantitation (LLOQ)) whose 63 participants of them in the VIMKUNYA group and 6 in the placebo group.
The immune response of 2 559 participants (immunogenicity evaluable population [IEP]) who received VIMKUNYA and 424 participants who received placebo was analysed. All participants from IEP were seronegative at baseline (pre-vaccination) for CHIKV neutralising antibodies. The comparison of the anti-CHIKV SNA response to VIMKUNYA and placebo at study visit days 8, 15, 22, and 183 as measured by clinically relevant difference in seroresponse rate and GMT is shown in Table 2 and Table 3.
Table 2: Anti-CHIKV SNA seroresponse rate (SRR) at visit days 8, 15, 22 and 183 for phase 3 Study 1 (12 to < 65 years of age) (immunogenicity evaluable population)
| Study day | SRR VIMKUNYA (N = 2 559) n/N (%)a [95% CI]b | SRR placebo (N = 424) n/N (%)a [95% CI]b | SRR difference [95% CI]c | p-valued |
| Day 8 | 1 169/2 510 (46.6%) [44.6%, 48.5%] | 2/419 (0.5%) [0.1%, 1.7%] | 46.1% [43.8%, 48.1%] | < 0.0001 |
| Day 15 | 2 355/2 434 (96.8%) [96.0%, 97.4%] | 3/395 (0.8%) [0.3%, 2.2%] | 96.0% [94.3%, 96.8%] | < 0.0001 |
| Day 22 | 2 503/2 559 (97.8%) [97.2%, 98.3%] | 5/424 (1.2%) [0.5%, 2.7%] | 96.6% [95.0%, 97.5%] | < 0.0001 |
| Day 183 | 1 967/2 301 (85.5%) [84.0%, 86.9%] | 6/401 (1.5%) [0.7%, 3.2%] | 84.0% [81.7%, 85.6%] | < 0.0001 |
CI = confidence interval; SNA = serum neutralising antibody, SRR = seroresponse rate
a n is the number of participants with seroresponse ≥ titre 100, divided by N, the total number of participants in the group.
b 95% CIs of seroresponse rates are based on the Wilson method.
c Seroresponse rate difference is (VIMKUNYA minus placebo); 95% CIs are based on the Newcombe hybrid score method. Statistical superiority to placebo and lower bound of the 2‑sided 95% CI on the difference in seroresponse rates between VIMKUNYA group and placebo group ≥ 70% (considered clinically significant).
d p-value is from a two-sided chi-square test of equality of seroresponse percentages between groups.
Table 3: Anti-CHIKV SNA geometric mean titre (GMT) at visit days 8, 15, 22 and 183 for phase 3 Study 1 (12 to < 65 years of age) (immunogenicity evaluable population)
| Study day | VIMKUNYA (N = 2 559) | Placebo (N = 424) | p-valuec |
| Day 8a |
| nb | 2 510 | 419 | |
| SNA GMT [95% CI] | 93.4 [87.2, 100.0] | 7.4 [6.5, 8.4] | < 0.0001d |
| Day 15a |
| nb | 2 434 | 395 | |
| SNA GMT [95% CI] | 1 095.8 [1 029.3, 1 166.7] | 7.6 [6.8, 8.6] | < 0.0001d |
| Day 22a |
| nb | 2 559 | 424 | |
| SNA GMT [95% CI] | 1 618.1 [1 522.1, 1 720.0] | 7.9 [7.0, 8.8] | < 0.0001 |
| Day 183a |
| nb | 2 301 | 401 | |
| SNA GMT [95% CI] | 337.7 [318.3, 358.4] | 8.2 [7.3, 9.1] | < 0.0001d |
GMT = geometric mean titre, IEP = immunogenicity evaluable population, N = total IEP, SNA = serum neutralising antibody.
For GMT results, values below lower limit of quantitation (LLOQ) of 15 were assigned the value LLOQ/2=7.5.
IEP: exposed participants who have no measurable anti-CHIKV SNA at Day 1, have an evaluable Day 22 serum sample result within analysis window (Day 19 through 27, inclusive), and have no exclusionary protocol deviations as defined prior to database lock or unblinding (as applicable).
a Day 8, 15, 22 and 183 corresponding to 7-,14-, 21- and 182-days following vaccination with VIMKUNYA, respectively.
b n is the number of participants with a sample result available at the indicated visit.
c Geometric mean titre estimates, together with their 95% CIs, are derived from an ANOVA model that includes site and treatment group as fixed effects, assuming normality of the log titres. Ratio of GMT and 95% CIs are derived from the same model. p-value tests equivalence of group GMT on the log scale (ie, ratio of GMT equal to 1).
d Nominal p-value (formal adjustments for multiple comparisons were not applied).
Study 2
This study was a phase 3, randomised, placebo-controlled, double-blind, parallel-group study design with two treatment groups (VIMKUNYA or placebo). This was a multicentre study in the US with 413 healthy participants ≥ 65 years of age enrolled. Participants were randomised in a 1:1 ratio to receive either a single 40 micrograms dose of VIMKUNYA or placebo. The target population was adults ≥ 65 years of age (mean age 71 years of age [range 65 to 95]) stratified by age subgroups (65 to < 75 (N = 318; 77%) and ≥ 75 years of age (N = 95; 23%)). In the randomised population, 171 (41%) participants were males and 242 (59%) were females. Participants in this study were followed up for 6 months after immunisation. There were 15 baseline seropositive participants (defined as Day 1 predose anti-CHIKV titre ≥ 15 (≥ lower limit of quantitation [LLOQ]) whose 5 participants of them in the VIMKUNYA group and 10 in the placebo group. The immunogenicity evaluable population included 372 participants, of which 189 participants received VIMKUNYA and 183 participants received placebo. All these participants were negative at baseline (pre-vaccination) for CHIKV neutralising antibodies.
The comparison of the anti-CHIKV SNA response to VIMKUNYA and placebo at study visit days 15, 22, and 183 as measured by clinically relevant difference in seroresponse rate and GMT is shown in Table 4 and Table 5.
Table 4: Anti-CHIKV SNA seroresponse rate (SRR) at visit days 15, 22 and 183 for phase 3 Study 2 (≥ 65 years of age) (immunogenicity evaluable population)
| Study day | SRR VIMKUNYA (N = 189) n/N (%)a [95% CI]b | SRR placebo (N = 183) n/N (%)a [95% CI]b | SRR difference [95% CI]c | p-valued |
| Day 15 | 149/181 (82.3%) [76.1%, 87.2%] | 5/176 (2.8%) [1.2%, 6.5%] | 79.5% [72.3%, 84.6%] | <0.0001 |
| Day 22 | 165/189 (87.3%) [81.8%, 91.3%] | 2/183 (1.1%) [0.3%, 3.9%] | 86.2% [80.0%, 90.3%] | <0.0001 |
| Day 183 | 139/184 (75.5%) [68.9%, 81.2%] | 2/173 (1.2%) [0.3%, 4.1%] | 74.4% [67.1%, 80.1%] | <0.0001 |
CI = confidence interval; SNA = serum neutralising antibody, SRR = seroresponse rate
a n is the number of participants with seroresponse ≥ titre 100, divided by N, the total number of participants in the group.
b 95% CIs of seroresponse rates are based on the Wilson method.
c Seroresponse rate difference is (VIMKUNYA minus placebo); 95% CIs are based on the Newcombe hybrid score method. Statistical superiority to placebo and lower bound of the two-sided 95% CI on the difference in seroresponse rates between VIMKUNYA group and placebo group ≥ 70% (considered clinically significant).
d p-value is from a two-sided chi-square test of equality of seroresponse percentages between groups.
Table 5: Anti-CHIKV SNA geometric mean titre (GMT) at visit days 15, 22 and 183 for phase 3 Study 2 (≥ 65 years of age) (immunogenicity evaluable population)
| Study day | VIMKUNYA (N = 189) | Placebo (N = 183) | p-valuec |
| Day 15a | |
| nb | 181 | 176 | |
| SNA GMT [95% CI] | 378.4 [301.0, 475.7] | 9.0 [7.1, 11.3] | <0.0001d |
| Day 22a | |
| nb | 189 | 183 | |
| SNA GMT [95% CI] | 723.9 [584.1, 897.2] | 8.1 [6.5, 10.0] | <0.0001 |
| Day 183a | |
| nb | 184 | 173 | |
| SNA GMT [95% CI] | 233.0 [194.1, 279.8] | 8.3 [6.9, 10.0] | <0.0001d |
GMT = geometric mean titre; IEP = immunogenicity evaluable population; N = total IEP, SNA = serum neutralising antibody.
For GMT results, values below lower limit of quantitation (LLOQ) of 15 were assigned the value LLOQ/2=7.5.
IEP: exposed participants who have no measurable anti-CHIKV SNA at Day 1, have an evaluable Day 22 serum sample result within analysis window (Day 19 through 27, inclusive), and have no exclusionary protocol deviations as defined prior to database lock or unblinding (as applicable).
a Day 15, 22 and 183 corresponding to 14-, 21- and 182-days following vaccination with VIMKUNYA, respectively.
b n is the number of participants with a sample result available at the indicated visit.
c Geometric mean titre estimates, together with their 95% CIs, are derived from an ANOVA model that includes site and treatment group as fixed effects, assuming normality of the log titres. Ratio of GMT and 95% CIs are derived from the same model. p-value tests equivalence of group GMT on the log scale (ie, ratio of GMT equal to 1).
d Nominal p-value (formal adjustments for multiple comparisons were not applied).
In the phase 3 studies (Study 1, Study 2), among the different age groups, the seroresponse rate (anti‑CHIKV SNA NT80 titre ≥ 100) and GMT measured in the VIMKUNYA group at Day 22 (21 days postvaccination) were as follows: 12 to < 18: 97.0%, GMT 2 502; 18 to < 46: 98.3%, GMT 1 878; 46 to < 65: 97.2%, GMT 1 175; ≥ 65 to < 75: 87.9%, GMT 726; and ≥ 75 years of age 85.0%, GMT 716.
Paediatric population
The European Medicines Agency has deferred the obligation to submit the results of studies with VIMKUNYA in one or more subsets of the paediatric population for active immunisation for the prevention of disease caused by chikungunya virus (CHIKV) (see section 4.2 for information on paediatric use).