Vaccine Information: Vaxchora (Page 3 of 4)

14.2 Immunogenicity

Vibriocidal Antibody Against the Vaccine Strain (classical Inaba)

A vibriocidal antibody assay was used to measure serum levels of neutralizing antibodies against the vaccine strain.

Study 2 was a randomized, double-blind, saline placebo-controlled V. cholerae challenge study conducted in adults 18 through 45 years of age. In the subset of subjects challenged in Study 2, 91% [95% CI 82%, 97%] of vaccinees seroconverted prior to challenge and 9% developed moderate to severe cholera following challenge, while 2% of placebo recipients seroconverted prior to challenge and 59% developed moderate to severe cholera following challenge. (Seroconversion was defined as a ≥ 4-fold rise in serum vibriocidal antibody from baseline to 10 days post-vaccination.) Based on the observed association between seroconversion and protection from V. cholerae disease, seroconversion rate at 10 days post-vaccination was used to evaluate response to vaccination in other age groups.

Study 1 was a randomized, double-blind, saline placebo-controlled safety and immunogenicity study conducted in the US and Australia. A total of 3146 subjects 18 through 45 years of age not previously exposed to cholera were randomized 8:1 to receive one dose of VAXCHORA or placebo. The mean age was 29.9 years; 45.2% were male; 68.3% were White, 25.6% were Black, 2.0% were Asian, 1.9% were multiracial, 1.4% were other, 0.4% were American Indian/Alaskan Native, and 0.3% were Native Hawaiian/Pacific Islander. There were 10.0% Hispanic or Latino participants.

In this study, classical Inaba vibriocidal antibody seroconversion rates were 93.5% [95% CI 92.5%, 94.4%] in vaccine recipients and 4% [95% CI 2%, 7%] in placebo recipients at 10 days post-vaccination.

Study 4 was a randomized, double-blind, placebo-controlled safety and immunogenicity study conducted in the US. A total of 398 subjects 46 through 64 years of age with no prior history of cholera infection or travel to a cholera-endemic area in the previous 5 years were randomized 3:1 to receive one dose of VAXCHORA or placebo. Overall, the mean age of the randomized population was 53.8 years; 45.7% were male; 74.9% were White, 21.9% were Black, 1.8% were American Indian/Alaskan Native, 0.5% were Asian, 0.5% were multiracial, 0.3% were Native Hawaiian/Pacific Islander, and 0.3% were other. There were 7.5% Hispanic or Latino participants.

Vibriocidal antibody seroconversion rates at 10 days post-vaccination for the classical Inaba strain among 46 through 64-year-old subjects in Study 4 were compared to those in 18 through 45-year-old subjects in Study 1. VAXCHORA recipients from Study 1 were in the same age group as those in Study 2, the V. cholerae challenge study.

Adults 46 through 64 years were shown to have a non-inferior rate of classical Inaba vibriocidal antibody seroconversion at 10 days post-vaccination compared to adults 18 through 45 years of age (Table 5).

Table 5: Vibriocidal Antibody Seroconversion Against Classical Inaba V. cholerae Vaccine Strain at 10 Days Post-Vaccination in Adults 46 through 64 Years of Age (Study 4) Compared to Adults 18 through 45 Years of Age (Study 1) [Bridging Analysis Population]
Studya Dose/CFU VAXCHORA Nb VAXCHORA Seroconversion %[95% CIc ]
a Data are derived from Study 1 (NCT02094586) and Study 4 (NCT02100631).b N=number of subjects with analyzable samples at Day 1 and Day 11.c CI=confidence interval.d Seroconversion is defined as the percentages of subjects who had at least a 4-fold rise in vibriocidal antibody titer at 10 days post-vaccination compared to baseline.e Pre-specified success criterion was that the lower bound of the two-sided 95% confidence interval on the difference in seroconversion rate (Study 4 minus Study 1) must be greater than -10 percentage points.

Study 4 (46 through 64-year-olds)

1 x 109

291

90.4%[86.4%, 93.5%]

Study 1 (18 through 45-year-olds)

1 x 109

2687

93.5%[92.5%, 94.4%]

Difference in Seroconversion Ratesd,e

-3.1%[-6.7%, 0.4%]

Vibriocidal Antibody Against Classical Ogawa, El Tor Inaba and El Tor Ogawa

V. cholerae serogroup O1 consists of four major subtypes: classical Inaba, classical Ogawa, El Tor Inaba and El Tor Ogawa. Serum vibriocidal antibody against the three types of V. cholerae not contained in the vaccine, namely classical Ogawa, El Tor Inaba and El Tor Ogawa, was also measured in Study 2 and Study 4. The percentages of vaccine recipients who seroconverted against each of the 4 major biotype/serotypes of V. cholerae serogroup O1 at 10 days post- vaccination (71.4% to 91.4%) are shown in Table 6.

Table 6: Seroconversion Rates 10 Days Post-Vaccination for the Four Major V. cholerae O1 Serogroup Biotypes and Serotypes in Studies 2 and 4 [Immunogenicity Evaluable Population]
Cholera Strain Study 2a (18 through 45-year-olds) VAXCHORA Nb Study 2a (18 through 45-year-olds) VAXCHORA %c [95% CId ] Study 4a (46 through 64-year-olds) VAXCHORA Nb Study 4a (46 through 64-year-olds) VAXCHORA %[95% CI]
a Data are derived from Study 2 (NCT01895855) and Study 4 (NCT02100631).b N=number of subjects with measurements at baseline and 10 days post-vaccination. One subject in Study 2 did not have a Day 11 measurement and was dropped from the analysis.c Seroconversion is defined as the percentages of subjects who had at least a 4-fold rise in vibriocidal antibody titer at 10 days post-vaccination compared to the titer measured at baseline.d CI=confidence interval.e VAXCHORA contains the classical Inaba strain of V. cholerae O1.

Classical Inabae

93

90.3%[82.4%, 95.5%]

291

90.4%[86.4%, 93.5%]

El Tor Inaba

93

91.4%[83.8%, 96.2%]

290

91.0%[87.1%, 94.1%]

Classical Ogawa

93

87.1%[78.5%, 93.2%]

291

73.2%[67.7%, 78.2%]

El Tor Ogawa

93

89.2%[81.1%, 94.7%]

290

71.4%[65.8%, 76.5%]

Pediatric Trial — Vibriocidal Antibody Against the Vaccine Strain (classical Inaba)

The effectiveness of VAXCHORA for the pediatric population 2 through 17 years of age was demonstrated following comparison of the immune response to V. cholerae in children and adolescents to the immune response in adults following Vaxchora (immunobridging).

Study 5 was a randomized, double-blind, saline placebo-controlled safety and immunogenicity study conducted in the US. A total of 550 subjects 2 through 17 years of age not previously exposed to cholera were randomized 6:1 to receive one dose of VAXCHORA (1 x 109 CFU/dose) or placebo. Randomization was stratified by age into 3 age cohorts:

Cohort 1: 12 to <18 years of age
Cohort 2: 6 to <12 years of age
Cohort 3: 2 to <6 years of age

In this study, classical Inaba vibriocidal antibody seroconversion rates at 10-days post-vaccination in children 2 through 17 years of age were compared to seroconversion rates in adults 18 through 45 years of age.

Immunobridging results for VAXCHORA, at 10 days post-vaccination, are shown in Table 7. The rate of seroconversion among pediatric placebo recipients was 1.5% [95% CI 0.3%, 8.0%] at 10 days post-vaccination.

Table 7: Vibriocidal Antibody Seroconversion Against Classical Inaba V. cholerae Vaccine Strain at 10 Days Post-Vaccination in Children aged 2 through 17 Years (Study 5) Compared to Adults 18 through 45 Years of Age (Study 1) [Bridging Analysis Populationb ]
a Data are derived from Study 1 (NCT02094586) and Study 5 (NCT03220737).b N=number of subjects with analyzable samples at Day 1 and Day 11 in the immunogenicity evaluable population.c CI=confidence interval.d Seroconversion is defined as the percentages of subjects who had at least a 4-fold rise in vibriocidal antibody titer at 10 days post-vaccination compared to baseline.e Pre-specified success criterion was that the lower bound of the two-sided 96.7% confidence interval on the difference in seroconversion rate (Study 5 minus Study 1) must be greater than -10 percentage points. Co-primary criterion required the lower limit of the 98.3% CI to be ≥ 70% for the VAXCHORA group.

Study a

Dose/CFU

VAXCHORA Nb

VAXCHORASeroconversion %[98.3% CIc ]

Study 5 (2 through 17-year-olds)

1 x 109

399

98.5%[96.2%, 99.4%]

Study 1 (18 through 45-year-olds)

1 x 109

2687

93.5%[92.3%, 94.6%]

Difference in Seroconversion Ratesd,e

5.0%[2.8%, 6.4%]

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