Vaccine Information: NOVAVAX COVID-19 Vaccine, Adjuvanted (Page 6 of 8)

18.3 Immunogenicity of a Booster Dose Following a Novavax COVID-19 Vaccine, Adjuvanted Primary Series in Participants 18 Years and Older

Effectiveness of a booster dose of the Novavax COVID-19 Vaccine, Adjuvanted was based on assessment of neutralizing antibody titers (MN50 ) against the original SARS-CoV-2 strain (SARS-CoV-2 hCoV-19/Australia/VIC01/2020). Immunogenicity analyses compared the MN50 titers following the booster dose to the MN50 titers following the primary series.

In the open-label booster phase of Study 1, participants 18 years of age and older received a single booster dose of the Novavax COVID-19 Vaccine, Adjuvanted at least 6 months after completion of the primary series. A subset of 243 participants were included in the per-protocol immunogenicity (PP-IMM) analysis set, did not have serologic or virologic evidence (if available) of SARS-CoV-2 infection up to 28 days post booster dose. Among participants assessed for immunogenicity, 87.2% were 18-64 years of age, 12.8 % were 65 years of age and older, 51.0% were males, 49.0% were female; 15.6% were Hispanic or Latino; 81.5% were White, 11.1% were Black or African American, 0.4% were American Indian or Alaska Native, 4.9% were Asian, and 1.6% were multiracial. The median age of participants was 52 years (range 19-79 years).

Prespecified immunogenicity non-inferiority analyses included an assessment of MN50 geometric mean titer (GMT) ratio and difference in seroconversion rates. Seroconversion for a participant was defined as achieving a 4-fold rise in MN50 from baseline (before the booster dose and before the first dose of the primary series).

The analysis of the GMT ratio of MN50 following the booster dose compared to the primary series met the non-inferiority criteria for a booster response (lower limit of the 95% CI > 0.67) and point estimate > 0.83.

The lower limit of the two-sided 95% CI for the difference in seroconversion rates was -14.4%, which did not meet the non-inferiority criteria for a booster response (lower limit of 95% CI for the percentage difference of ≥ -10%). These analyses are summarized in Table 8 and Table 9.

Table 8 Neutralizing Antibody Geometric Titers (MN50 ) Against the Original SARS-CoV-2 Virus Strain (SARS CoV-2 hCoV-19/Australia/VIC01/2020) at 28 Days after a Booster Dose Versus 14 Days After Completion of the Primary Series, Participants ≥ 18 Years of Age, PP-IMM Analysis Set *
Booster Dose(N = 239)GMT(95% CI) Primary Series(N = 239)GMT(95% CI) GMT Ratio(Booster/Primary Series)(95% CI)* Met Success Criteria
Abbreviations: CI = confidence interval; GMT = geometric mean titer; MN50 = microneutralization assay with an inhibitory concentration of 50%; PP-IMM = Per-Protocol Immunogenicity.
Note: The median duration between the time of the second dose of the Novavax COVID-19 Vaccine, Adjuvanted and the time of the booster dose was 10 months.
*
PP-IMM Analysis Set included participants who received two doses (0.5 mL 3 weeks apart) of the Novavax COVID-19 Vaccine, Adjuvanted in the initial vaccination period or in the blinded crossover vaccination period, had an immunogenicity blood sample collected at Day 35, did not have serologic or virologic evidence (if available) of SARS-CoV-2 infection up to 28 days post booster dose, did not receive an emergency use authorized COVID-19 vaccine, received the booster dose, and remained blinded on study and without major protocol deviations until 7 days post-crossover Dose.
The analysis included a total of 239 participants of the PP-IMM analysis set who had immunogenicity data available for both the booster and primary series.
The 95% CI for GMT and GMT ratio were calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation.
5075.6(4448.3, 5791.4) 1505.7(1244.1, 1822.3) 3.4(2.8, 4.0) Lower limit of 95% CI > 0.67 and point estimate > 0.83 criteria: Yes
Table 9 Seroconversion Rates Against the Original SARS-CoV-2 Strain (SARS-CoV-2 hCoV-19/Australia/VIC01/2020) at 28 Days after a Booster Dose Versus 14 Days After Completion of the Primary Series, Participants ≥ 18 Years of Age, PP-IMM Analysis Set *
Booster Dose(N = 239)SCRn (%)(95% CI) Primary Series(N = 239)SCRn (%)(95% CI) Difference in SCR §(Booster-Primary Series)(95% CI) Met Success Criteria #
Abbreviations: CI = confidence interval; PP-IMM = Per-Protocol Immunogenicity; SCR = seroconversion rate.
Note: SCR was defined as the proportion of participants with post-vaccination levels ≥ 4-fold higher than the baseline levels.
Note: The median duration between the time of the second dose of the Novavax COVID-19 Vaccine, Adjuvanted and the time of the booster dose was 10 months.
*
PP-IMM Analysis Set included participants who received two doses (0.5 mL 3 weeks apart) of the Novavax COVID-19 Vaccine, Adjuvanted in the initial vaccination period or in the blinded crossover vaccination period, had an immunogenicity blood sample collected at Day 35, did not have serologic or virologic evidence (if available) of SARS-CoV-2 infection up to 28 days post booster dose, did not receive an emergency use authorized COVID-19 vaccine, received the booster dose, and remained blinded on study and without major protocol deviations until 7 days post-crossover Dose 2.
The analysis included a total of 239 participants of the PP-IMM analysis set who had immunogenicity data (microneutralization) available for both the booster and primary series
95% CI is based on the Clopper-Pearson method.
§
Based on the Tango method.
Comparison between SCR of 28 days post-booster relative to time of booster and SCR of 14 days after second dose of the primary series relative to time of first dose.
#
Non-inferiority of the single booster dose was achieved if the lower limit of the 95% CI for the difference of the proportion of participants with SCR at 28 days after a single booster dose relative to the time of booster vaccination versus at 14 days after the second dose of the Novavax COVID-19 Vaccine, Adjuvanted relative to the time of first vaccination was > -10%.
204 (85.4)(80.2, 89.6) 226 (94.6)(90.9, 97.1) -9.2%(-14.4%, -4.5%) Lower limit of 95% CI > -10% criterion: No

An additional descriptive analysis evaluated seroconversion rates using baseline neutralizing antibody titers prior to Dose 1 of the primary series. As shown in Table 10, the booster dose seroconversion rate, with seroconversion defined as at least a 4-fold rise relative to the time of first dose, was 98.3%. The difference in seroconversion rates in this post-hoc analysis was 3.8% (95% CI: 2.0%, 7.0%).

Table 10 Analysis of Seroconversion Rates Against the Original SARS-CoV-2 Strain (SARS CoV-2 hCoV-19/Australia/VIC01/2020) at 28 Days after a Booster Dose Versus 14 Days After Completion of the Primary Series, Participants ≥ 18 Years of Age, PP-IMM Analysis Set *
Booster Dose(N = 239)SCRn (%)(95% CI) Primary Series(N = 239)SCRn (%)(95% CI) Difference in SCR §(Booster-Primary Series)(95% CI)
Abbreviations: CI = confidence interval; PP-IMM = Per-Protocol Immunogenicity; SCR = seroconversion rate.
Note: SCR was defined as the proportion of participants with post-vaccination levels ≥ 4-fold higher than at the time of the first dose.
Note: The median duration between the time of the second dose of the Novavax COVID-19 Vaccine, Adjuvanted and the time of the booster dose was 10 months.
*
PP-IMM Analysis Set included all participants who received two doses (0.5 mL 3 weeks apart) of the Novavax COVID-19 Vaccine, Adjuvanted in the initial vaccination period or in the blinded crossover vaccination period, had an immunogenicity blood sample collected at Day 35, did not have serologic or virologic evidence (if available) of SARS-CoV-2 infection up to 28 days post booster dose, did not receive an emergency use authorized COVID-19 vaccine, received the booster dose, and remained blinded on study and without major protocol deviations until 7 days post-crossover Dose 2.
The analysis included a total of 239 participants of the PP-IMM analysis set who had immunogenicity data (microneutralization) available for both the booster and primary series
95% CI is based on the Clopper-Pearson method.
§
Based on the Tango method.
Comparison between SCR of 28 days post-booster relative to time of first dose and SCR of 14 days after second dose of the primary series relative to time of first dose.
235 (98.3)(95.8, 99.5) 226 (94.6)(90.9, 97.1) 3.8%(2.0%, 7.0%)

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