Vaccine Information: NOVAVAX COVID-19 Vaccine, Adjuvanted (Page 5 of 8)

18.2 Effectiveness of a Two-Dose Primary Series in Adolescents 12 Through 17 Years of Age

Effectiveness in adolescents 12 years through 17 years of age is based on a comparison of immune responses in this age group to adults 18 years through 25 years of age.

Study 1 is an ongoing Phase 3 multicenter, randomized, observer-blinded, placebo-controlled study that included 2,247 participants 12 through 17 years of age in the United States. Participants were randomized in a 2:1 ratio to receive two doses of the Novavax COVID-19 Vaccine, Adjuvanted or placebo 3 weeks apart. The study excluded participants who were significantly immunocompromised due to immunodeficiency disease; had active cancer on chemotherapy; had received chronic immunosuppressive therapy or had received immunoglobulin or blood-derived products within 90 days; were pregnant or breastfeeding; or had a history of laboratory-confirmed diagnosed COVID-19. Participants with clinically stable underlying comorbidities and participants with well-controlled HIV infection were included.

In Study 1, an analysis was conducted of SARS-CoV-2 neutralizing antibody titers 14 days after Dose 2 in a subset of adolescents 12 through 17 years of age and participants 18 through 25 years of age from the adult main study. Noninferior immune responses as assessed by geometric mean titers and seroconversion rates were demonstrated in a comparison of adolescents 12 through 17 years of age to participants 18 through 25 years of age (Table 6).

Table 6 SARS-CoV-2 Neutralizing Antibody Geometric Mean Titer Ratio and Seroconversion Rate – Comparison of Adolescents 12 Years Through 17 Years of Age to Participants 18 Years Through 25 Years of Age – Per-Protocol Immunogenicity Analysis Set
Assays TimePoint 12 Years Through 17 Years 18 Years Through 25 Years 12 Years Through 17 Years/18 Years Through 25 Years
GMT *(95% CI)n=390 GMT *(95% CI)n=415 GMR †(95% CI) Met NoninferiorityCriteria ‡
CI = Confidence interval; GMR = Geometric mean ratio; GMT = Geometric mean titer; SCR = Seroconversion rate
*
The 95% CI for GMT is calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation.
†
GMR is defined as the ratio of two geometric mean titers for comparison of two age cohorts. An analysis of covariance (ANCOVA) with age cohort as main effect and baseline microneutralization assay neutralizing antibodies as covariate was performed to estimate the GMR.
‡
Noninferiority was achieved if the following 3 pre-specified criteria were met simultaneously: 1) Lower bound of two-sided 95% CI for the ratio of GMTs (GMT12-17yo /GMT18-25yo ) > 0.67; 2) Point estimate of the ratio of GMTs ≥ 0.82; and 3) Lower bound of the two-sided 95% CI for difference of SCRs (SCR12-17yo — SCR18-25yo ) was > -10%.
§
Validated virus neutralizing assay (VNA) with wild-type virus (SARS-CoV-2 hCoV-19/Australia/VIC01/2020 [GenBank MT007544.1]; 360biolabs, Melbourne, Australia). The lower limit for quantification for this assay was a titer of 20, with titers below this level documented as 10.
SCR is defined as percentage of participants with a ≥ 4-fold difference in titers between Day 35 and Day 0. The 95% CI for SCR was calculated using the Clopper-Pearson exact method.
#
Difference in SCR in the adolescent primary series expansion (Study 1) for 12 years through 17 years of Study 1 minus SCR in Adult Main Study (Study 1) for 18 years through 25 years. The 95% CI for the difference of SCR between groups was calculated with the method of Miettinen and Nurminen.
SARS-CoV-2 wild-typemicroneutralization assay (1/dilution)§ 14 daysafterDose 2 3859.6 (3422.8, 4352.1) 2611.8 (2367.4, 2881.5) 1.47 (1.26, 1.72)3 Yes
SCR%(95% CI) n=385 SCR%(95% CI)n=414 Difference inSCR%# (95% CI)
98.7 (97.0, 99.6) 99.8 (98.7, 100.0) -1.04 (-2.75, 0.20)

A descriptive efficacy analysis evaluating PCR-confirmed symptomatic mild, moderate or severe COVID-19 cases was performed in 1,799 participants who were included in the per-protocol efficacy (PP-EFF) Analysis Set, which required receipt of two doses (Dose 1 on day 0; Dose 2 on day 21), no exclusionary protocol deviation(s), and no evidence of SARS-CoV-2 infection through 6 days after the second dose. In the PP-EFF Analysis Set, 47.2% were female; 15.8% were Hispanic or Latino; 76.1% were White, 12.9% were Black or African American, 1.1% were American Indian or Alaska Native, 3.6% were Asian, and 5.6% were multiracial. The median age of participants was 14 years (range 12-17 years). Of the study participants in the PP-EFF Analysis Set, 25.3% were obese. Between participants who received the Novavax COVID-19 Vaccine, Adjuvanted and those who received placebo, there were no notable differences in demographics. The median interval between doses of study vaccine was 22 days (range 14-43). As of the August 9, 2021, data cutoff date, the PP-EFF Analysis Set had a median follow-up of 67 days post-Dose 2 during the pre-crossover period.

Vaccine efficacy in participants without evidence of SARS-CoV-2 infection through 6 days after the second dose is presented in Table 7. Based on data accrued through August 9, 2021, the efficacy of the Novavax COVID-19 Vaccine, Adjuvanted to prevent PCR-confirmed symptomatic mild, moderate or severe COVID-19 from 7 days after Dose 2 was 78.29% (95% CI: 37.55%, 92.45%). No cases of moderate or severe COVID-19 were reported in participants who had received the Novavax COVID-19 Vaccine, Adjuvanted or placebo.

Table 7 Vaccine Efficacy Against PCR-confirmed COVID-19 with Onset from 7 Days After Second Vaccination * (PP-EFF Analysis Set)
Subgroup Novavax COVID-19 Vaccine, Adjuvanted Placebo Vaccine Efficacy (95% CI) (%)
Partici-pantsN COVID-19 Cases †n (%) Mean Incidence Rate Per 100 Person-Years Partici-pantsN COVID-19 Cases †n (%) Mean Incidence Rate Per 100 Person-Years
*
Vaccine efficacy (VE) evaluated in participants without major protocol deviations who were seronegative (for SARS-CoV-2) at baseline and did not have a laboratory confirmed current SARS-CoV-2 infection with symptom onset through 6 days after the second dose, and who had received two doses of vaccine or placebo as randomized.
†
All cases for which sequence data are available (vaccine n=2; placebo n=7) were due to the Delta variant.
‡
Based on Modified Poisson regression with logarithmic link function and treatment group as fixed effect and robust error variance (Zou 2004).
Primary efficacy endpoint
All participants 1205 5 (0.4) 2.69 594 11 (1.9) 12.38 78.29(37.55, 92.45)‡
Mild – 5 (0.4) – – 11 (1.9) – –
Moderate – 0 – – 0 – –
Severe – 0 – – 0 – –

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