Study design and participants
This is an interim analysis of an ongoing phase 2, prospective, double-blind (investigator/site staff and participants), and multi-center study to assess the safety and immunogenicity of MVC-COV1901 in adolescents aged 12 to 17 years. The study sites included five hospitals/medical centers in Taiwan. Eligible participants were those aged 12 (inclusive) to 17 (not legible if the participant turned 18 years old) at the time of randomization, with body mass index (BMI) at or above the third percentile according to World Health Organization (WHO) at the screening visit, and lack of travel within 14 days of screening and lack of any oversea travelling throughout the study period. Finally, participant and/or the participant’s legal representative must have provided written informed consent. Additional criteria applied to females only: negative pregnancy test, non-childbearing potential or, if with childbearing potential, abstinence or agreement to use medically effective contraception from 14 days before screening to 30 days following the last injection of study intervention. A full list of inclusion and exclusion criteria can be found in the study protocol in the Appendix.
The trial protocol and informed consent form were approved by Taiwan Food and Drug Administration (TFDA) and the ethics committees at the conducting sites: Mackay Memorial Hospital Hsinchu (Hsinchu City), Chang-Gung Memorial Hospital Linkou (New Taipei City), Mackay Memorial Hospital (Taipei City), National Taiwan University Hospital Hsinchu (Hsinchu City), and National Taiwan University Hospital (Taipei City). An Independent Data Monitoring Committee (IDMC) was established to monitor data safety and trial conduct. The study complies with the protocol and statistical analysis plan. This trial was conducted in accordance with the principles of the Declaration of Helsinki and Good Clinical Practice (GCP) guidelines.
Randomization and blinding
All eligible participants were randomized to receive either MVC-COV1901 or placebo in a 6:1 ratio. All participants were centrally assigned to randomized study intervention using an interactive web response system (IWRS). Before the study was initiated, the log-in information and directions for the IWRS were provided to each site.
This was a double-blind study in which participants and investigators were blinded to study intervention. The IWRS was programmed with blind-breaking instructions and in case of an emergency, the investigator had the sole responsibility for determining if unblinding of participants’ intervention assignment was warranted. For the interim analysis, an independent, unblinded team of the CRO consisting of personnel representing relevant functions, including statistics, programming, and report writing, was involved in the activity of the interim analysis. All activities of the unblinded team were separated from the main blinded team of the study. The Sponsor was blinded until the time of the interim analysis.
As MVC-COV1901 and placebo were visually distinct in their color of appearance, the investigator had assigned unblinded qualified personnel who were not involved in any other aspect of the study to handle the preparation, dispensing, administration, and accountability of the study intervention. Study-specific training was provided to the study site to ensure treatment blinding of all other study staff and the participants.
The study schedule is outlined as in Figure S1. The participants were intramuscularly administered in the deltoid region with two doses of either MVC-COV1901 or placebo (saline) on Day 1 (Visit 2) and Day 29 (Visit 4). The vaccine MVC-COV1901 and placebo were produced at Medigen Vaccine Biologics Zhubei facility (Hsinchu County, Taiwan) in compliance with current good manufacturing practices. MVC-COV1901 contained 15 µg S-2P, 750 µg CpG 1018, and 375 µg aluminum hydroxide at a final volume of 0.5 mL per dose. The placebo contained 0.5 mL of saline solution per dose. Participant samples were collected during six on-site visits: on Days – 28 to 0 (screening Visit), 1 (first vaccination), 29 (second vaccination), 57, 119, and 209. Safety data was monitored by three telephone calls on Days 8, 36, and 85.
For safety analysis, vital signs were assessed before and after each injection. Participants were observed for at least 30 minutes after each injection to identify any immediate adverse events. All participants who received at least one of the two doses of MVC-COV19 scheduled for Day 1 and Day 29 were evaluated for safety up to Day 119 (Visit 8) by assessing the following endpoints: solicited local adverse events (AEs) (up to 7 days after each dose of study intervention), solicited systemic AEs (up to 7 days after each dose of study intervention), unsolicited AEs (up to 28 days after each dose of study intervention), AEs of special interest (AESI), vaccine-associated enhanced disease (VAED) and serious adverse events (SAEs). Solicited AEs were defined as AEs which occurred within 7 days after each dose of study intervention, including local events: pain/tenderness, erythema/redness, and induration/swelling; systemic events: fever, malaise/fatigue, myalgia, headache, nausea/vomiting, and diarrhea. Unsolicited AEs are defined as any untoward medical events other than solicited AEs which occurred within 28 days after each dose of study intervention. The intensities of solicited and unsolicited AEs were graded using grading scales modified from the US FDA Guidance for Industry .
To evaluate immunogenicity, live SARS-CoV-2 neutralization assay and anti-SARS-CoV-2 spike immunoglobulin (IgG) ELISA were used as previously reported [15, 17]. Briefly, serially two-fold diluted sera were mixed with an equal volume of SARS-CoV-2 virus (hCoV-19/Taiwan/4/2020, GISAID accession ID: EPI_ISL_411927). The serum-virus mixture was incubated and then added to the plates containing Vero E6 cells, followed by further incubation. The neutralizing antibody titer was defined as the reciprocal of the highest dilution capable of inhibiting 50% of the cytopathic effect (50% inhibiting dilution, ID50), which was calculated using the Reed-Muench method. For anti-SARS-CoV-2 spike IgG ELISA, antigen-specific immunoglobulin titers to S-2P protein were evaluated in serum samples collected from participants. The detection and characterization of antigen-specific immunoglobulin were performed by a central laboratory using a validated enzyme-linked immunosorbent assay (ELISA) method with plates coated with S-2P proteins .
For standardization of results, the geometric mean titers (GMTs) of ID50 from the neutralization assay were converted to International Units (IUs/mL) in the following transformations defined experimentally: y = 1.5001 ∙ x0.8745 for the adolescent data and y = 0.4964 ∙ x1.0334 for the young adult data, where y is the value of IU/mL and x is the value of the GMT. Similarly, the GMTs from the ELISA assay were converted to Binding Antibody Unit (BAUs/mL) as previously established by multiplying by a factor of 0.0912 .
The primary safety outcome included the occurrence rate of solicited (local and systemic) AEs, unsolicited AEs, AESI, VAED, and SAE from Visit 2 (Day 1) to Visit 6 (28 days after second dose of study intervention). The primary immunogenicity outcomes were neutralizing antibody titers and seroconversion rate (SCR) against live SARS-CoV-2 virus of MVC-COV1901 in adolescents as compared to young adult vaccinees at Visit 6 (Day 57).
The secondary safety outcome included the occurrence rate of ≥ Grade 3 AE, AESI, VAED, and SAE over the whole study period i.e. from Day 1 to 180 days after the second vaccination (Day 209). For secondary immunogenicity outcomes, comparisons of MVC-COV1901 against placebo were performed by measuring and expressing antigen-specific immunoglobulin titers and neutralizing antibody titers in samples taken at Visit 4 (28 days after the first dose of study intervention), Visit 6 (28 days after the second dose of study intervention), Visit 8 (90 days after the second dose of study intervention) and Visit 9 (209 days after the second dose of study intervention).
Three hundred and ninety-nine participants were randomly assigned to study intervention. The sample size was powered to demonstrate that the immunogenicity of MVC-COV1901 in adolescents is non-inferior to that in young adults assessed by neutralizing antibody GMT and seroconversion rate (SCR) 28 days after second dose of study intervention. Demographical and immunogenicity data of young adults (20–30 years old, who were seronegative for SARS-CoV-2 neutralizing antibody at baseline and received MVC-COV1901), were selected from a previous phase 2 trial for comparison .
Safety was analyzed with the safety set population, which consisted of all randomized participants who received at least one dose of study intervention. Immunogenicity was analyzed with the per protocol set (PPS) population, which consisted of the individuals who received the planned doses of randomized study intervention per schedule, were seronegative at baseline (neutralizing antibody titer < lower limit of detection at Visit 2), anti-N antibodies negative at Visit 2 and Visit 6, and did not have a major protocol deviations that were judged to impact the critical or key study data.
Seroconversion was defined as at least 4-fold increase of post-study intervention antibody titers from the baseline titer or from half of the lower limit of detection (LoD) if undetectable at baseline. Immunogenicity results were presented as GMTs, GMT ratios, and SCRs with two-sided 95% CIs.
The GMT ratio and two-sided 95% CIs were calculated by exponentiating the mean difference of the logarithms of the titers (the adolescent group cohort minus the young adult group) and the corresponding confidence intervals (based on the two samples t-test). For SCR, chi-square test was used to compare between the two treatment arms.
Immunogenicity primary endpoints were the non-inferiority of neutralizing antibody GMT ratio and SCR at 28 days after second dose of MVC-COV1901 in adolescents compared to young adults. The adolescent group was claimed as non-inferior to young adult group in GMT treatment ratio when the lower bound of the two-sided 95% CI of GMT treatment ratio is greater or equal to 0.67. The adolescent group was deemed as non-inferior to young adults group in SCR treatment difference when the lower bound of the two-sided 95% CI of SCR treatment difference is greater or equal to -10%
The secondary immunogenicity endpoints of study intervention included the GMT, SCR, and GMT ratio of antigen-specific immunoglobulin titers and neutralizing antibody titers at Visit 4 (28 days after the first dose of study intervention), Visit 6 (28 days after the second dose of study intervention), Visit 8 (90 days after the second dose of study intervention) and Visit 9 (180 days after the second dose of study intervention). Only the results at Visit 4 and Visit 6 were available for the interim results. GMT ratio in secondary immunogenicity endpoint was defined as geometric mean of fold increase of post-study intervention titers over the baseline titers.