A Study of S-268019 for the Prevention of COVID-19

Participants without evidence of infection before vaccination (that is, seronegative and PCR-negative at baseline) were determined to have symptomatic COVID-19 when at least 1 protocol-specified COVID-19-related symptom and a positive RT-PCR test result were confirmed by the medical monitor within at least 14 days following the second vaccination. RT-PCR testing was based upon nasopharyngeal swab sampling at protocol-specified timepoints.

For participants without evidence of infection before vaccination (that is, seronegative and PCR-negative at baseline) who were confirmed to have symptomatic COVID-19 within at least 14 days following the second vaccination, the investigator evaluated if the maximum intensity during the course of the disease met protocol-specified criteria for severe COVID-19.

Participants without evidence of infection before vaccination (that is, seronegative and PCR-negative at baseline) were determined to have symptomatic COVID-19 when at least 1 protocol-specified COVID-19-related symptom and a positive RT-PCR test result were confirmed by the medical monitor. RT-PCR testing was based upon nasopharyngeal swab sampling at protocol-specified timepoints.

For participants without evidence of infection before vaccination (that is, seronegative and PCR-negative at baseline) who were confirmed to have symptomatic COVID-19, the investigator evaluated if the maximum intensity during the course of the disease met the protocol-specified criteria for severe COVID-19.

A participant was determined to have symptomatic COVID-19 when at least 1 protocol-specified COVID-19-related symptom and a positive RT-PCR test result were confirmed by the medical monitor within at least 14 days following the second vaccination. RT-PCR testing was based upon nasopharyngeal swab sampling at protocol-specified timepoints.

For participants confirmed to have symptomatic COVID-19 within at least 14 days following the second vaccination, the investigator evaluated if the maximum intensity during the course of the disease met the protocol-specified criteria for severe COVID-19.

A participant was determined to have symptomatic COVID-19 when the participant had at least 1 protocol-specified COVID-19-related symptom and a positive RT-PCR test result confirmed by the medical monitor. RT-PCR testing was based upon nasopharyngeal swab sampling at protocol-specified timepoints.

For participants confirmed to have symptomatic COVID-19, the investigator evaluated if the maximum intensity during the course of the disease met the protocol-specified criteria for severe COVID-19.

For participants without evidence of infection before vaccination (that is, seronegative and PCR-negative at baseline), asymptomatic SARS-CoV-2 infection was defined as having a positive result of anti-SARS-CoV-2 N-protein antibody test beginning 14 days following the second vaccination and not meeting the protocol-specified criteria of symptomatic COVID-19. Antibodies to SARS-CoV-2 N-protein were used to determine both natural infection and the incidence of asymptomatic infection acquired during the initial vaccination period of the study.

An adverse event (AE) was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Solicited systemic AEs were defined as the AEs that occurred within the first 7 days after each vaccination and were classified as one of the following: fever, nausea/vomiting, diarrhea, headache, fatigue, and myalgia. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Solicited local AEs were defined as the AEs that occurred within the first 7 days after each vaccination and were classified as one of the following: pain, erythema/redness, induration, and swelling. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.

Blood samples for immunogenicity assessments were collected during protocol-specified study visits. The serum neutralizing antibody level against SARS-CoV-2 was measured by a live virus neutralization assay. The GMT was calculated by taking the back transformation of the arithmetic mean of log-transformed titers. The 95% confidence interval was calculated based on the Student's t distribution of the log-transformed values, then back transformed to the original scale.

Blood samples for immunogenicity assessments were collected during protocol-specified study visits. The serum neutralizing antibody level against SARS-CoV-2 was measured by a live virus neutralization assay. The GMFR was calculated by taking the back transformation of the arithmetic mean of the change from baseline in log-transformed titers. The 95% confidence interval was calculated based on the Student's t distribution of the change from baseline in the log-transformed values, then back transformed to the original scale.

Blood samples for immunogenicity assessments were collected during protocol-specified study visits. The serum neutralizing antibody level against SARS-CoV-2 was measured by a live virus neutralization assay. Seroconversion was defined as a 4-times or higher from baseline in SARS-CoV-2 neutralizing antibody titer, where titer values reported as below the lower limit of quantification (LLOQ) were replaced by 0.5*LLOQ. Seroconversion rate was defined as the percentage of participants that underwent seroconversion. The 95% confidence interval was calculated using the Clopper-Pearson method.

Blood samples for immunogenicity assessments were collected during protocol-specified study visits. The serum neutralizing antibody level against SARS-CoV-2 (anti-spike protein IgG antibody) was measured by a chemiluminescence immunoassay. The GMT was calculated by taking the back transformation of the arithmetic mean of log- transformed titers. The 95% confidence interval was calculated based on the Student's t distribution of the log-transformed values, then back transformed to the original scale.

Blood samples for immunogenicity assessments were collected during protocol-specified study visits. The anti-spike protein IgG antibody was measured by a chemiluminescence immunoassay. The GMFR was calculated by taking the back transformation of the arithmetic mean of the change from baseline in log-transformed titers. The 95% confidence interval was calculated based on the Student's t distribution of the change from baseline in the log-transformed values, then back transformed to the original scale.

Blood samples for immunogenicity assessments were collected during protocol-specified study visits. The anti-spike protein IgG antibody was measured by a chemiluminescence immunoassay. Seroconversion was defined as a 4-times or higher from baseline in anti-spike protein IgG antibody titer, where titer values reported as below the LLOQ are replaced by 0.5*LLOQ and titer values reported as above the upper limit of quantification (ULOQ) are imputed at the ULOQ value. Seroconversion rate was defined as the percentage of participants that underwent seroconversion. The 95% confidence interval was calculated using the Clopper-Pearson method.