Antibody values reported as below the lower limit of quantification (LLOQ) were replaced by 0.5\*LLOQ. Values greater than the upper limit of quantification (ULOQ) were replaced by the ULOQ if actual values were not available. LLOQ was 103 arbitrary units (AU)/milliliter (mL) and ULOQ was 28571 AU/mL.

Seroresponse was defined as an antibody value change from baseline below the LLOQ to ≥4\*LLOQ, or at least a 4-fold rise if baseline was ≥LLOQ and \<4\*LLOQ, or at least a 2-fold rise if baseline was ≥4\*LLOQ, where baseline referred to pre-booster. LLOQ was 103 AU/mL and ULOQ was 28571 AU/mL.

Antibody values reported as below the LLOQ were replaced by 0.5\*LLOQ. Values greater than the ULOQ were replaced by the ULOQ if actual values were not available. LLOQ was 10 AU/mL and ULOQ was 111433 AU/mL.

Seroresponse was defined as an antibody value change from baseline below the LLOQ to ≥4\*LLOQ, or at least a 4-fold rise if baseline was ≥LLOQ and \<4\*LLOQ, or at least a 2-fold rise if baseline was ≥4\*LLOQ, where baseline referred to pre-booster. LLOQ was 10 AU/mL and ULOQ was 111433AU/mL.

CDC COVID-19 definition: the presence of at least 1 CDC listed symptom and positive reverse transcriptase polymerase chain reaction (RT-PCR) test on a respiratory sample.

Solicited ARs were recorded daily using electronic diaries (eDiaries). Local ARs: injection site pain, erythema (redness), swelling/induration (hardness); and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Note, not all solicited ARs were considered adverse events (AEs). Investigator reviewed whether the solicited AR was also to be recorded as an AE. A Summary of serious AEs (SAEs) and nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

Solicited ARs were recorded daily using eDiaries. Local ARs: injection site pain, erythema (redness), swelling/induration (hardness); and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Note, not all solicited ARs were considered AEs. Investigator reviewed whether the solicited AR was also to be recorded as an AE. A Summary of SAEs and nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

An unsolicited AE was defined as any AE reported by the participant that was not specified as a solicited AR in the protocol. An AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.

An unsolicited AE was defined as any AE reported by the participant that was not specified as a solicited AR in the protocol. An AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.

SAEs were AEs that resulted in death, were life threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions, a congenital anomaly or birth defect, or was a medically important event. MAAEs were AEs that lead to an unscheduled visit to a healthcare provider. AESIs were AEs (serious or nonserious) of scientific and medical concern specific to the Sponsor's product or program for which ongoing monitoring and immediate notification by the investigator to the Sponsor was required. AEs leading to the withdrawal from study reported for this endpoint also include the AEs that led to death. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.

SAEs were AEs that resulted in death, were life threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions, a congenital anomaly or birth defect, or was a medically important event. MAAEs were AEs that lead to an unscheduled visit to a healthcare provider. AESIs were AEs (serious or nonserious) of scientific and medical concern specific to the Sponsor's product or program for which ongoing monitoring and immediate notification by the investigator to the Sponsor was required. AEs leading to the withdrawal from study reported for this endpoint also include the AEs that led to death. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.