A Study to Evaluate the Immunogenicity and Safety of mRNA Vaccine Boosters for SARS-CoV-2 (COVID-19) Variants

GMFR of serum pseudovirus nAb ID50 titers against SARS-CoV-2 XBB.1.5, BA.4/BA.5, and SARS-CoV-2 BQ.1.1 at Day 15 is reported. GMFR measures the changes in immunogenicity titers or levels from Baseline within participants. 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. Antibody values reported as below the LOD are replaced by 0.5 \* LOD. LOD was 10 AU/mL for ID50 titer against XBB.1.5 and BQ.1.1. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 15

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

GMT of serum pseudovirus nAb ID50 titers against Omicron BA.1 Variant (B.1.1.529) and ancestral severe acute respiratory syndrome coronavirus (SARS-CoV-2) (D614G) at Day 29 is reported. mRNA-1273.214 (50 μg) as a second booster dose (Part A.2) was compared to mRNA-1273.211 (50 μg) as the first booster dose (Part A.1). 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 19.85 arbitrary units (AU)/milliliter (mL) and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous human immunodeficiency virus (HIV) infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. Overall number of participants analyzed = participants evaluable for this outcome measure.

GMFR of serum pseudovirus nAb ID50 titers against SARS-CoV-2 XBB.1.5, BA.4/BA.5, and SARS-CoV-2 BQ.1.1 at Day 29 is reported. GMFR measures the changes in immunogenicity titers or levels from Baseline within participants. 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. Antibody values reported as below the LOD are replaced by 0.5 \* LOD. LOD was 10 AU/mL for ID50 titer against XBB.1.5 and BQ.1.1. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5

Time frame: Day 29

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

GMT of serum pseudovirus nAb ID50 titers against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 181 is reported. mRNA-1273.214 (50 μg) as a second booster dose (Part A.2) was compared to mRNA-1273.211 (50 μg) as the first booster dose (Part A.1). 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 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

GMT of serum pseudovirus nAb ID50 titers against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 29 is reported. mRNA-1273.214 (Part G) was compared the mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). 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 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

GMT of serum pseudovirus nAb ID50 titers against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 91 is reported. mRNA-1273.214 (Part G) was compared the mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). 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 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 91

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

GMT of serum pseudovirus nAb ID50 titers against Omicron BA.1 Variant (B.1.1.529) at Day 29 is reported. Part F (Cohort 2) mRNA-1273.529 50 μg was compared to Part F (Cohort 2) mRNA-1273 50 μg. 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 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

GMT of serum pseudovirus nAb ID50 titers against BA.4/BA.5 and ancestral SARS-CoV-2 (D614G) at Day 29 is reported. mRNA-1273.222 (Part H) was compared to mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). 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 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

GMT of serum pseudovirus nAb ID50 titers against SARS-CoV-2 XBB.1.5, BA.4/BA.5, and SARS-CoV-2 BQ.1.1 at Day 15 is reported. 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. Antibody values reported as below the lower limit of detection (LOD) are replaced by 0.5 \* LOD. LOD was 10 AU/mL for ID50 titer against XBB.1.5 and BQ.1.1. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 15

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

GMT of serum pseudovirus nAb ID50 titers against SARS-CoV-2 XBB.1.5, BA.4/BA.5, and SARS-CoV-2 BQ.1.1 at Day 29 is reported. 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. Antibody values reported as below the LOD are replaced by 0.5 \* LOD. LOD was 10 AU/mL for ID50 titer against XBB.1.5 and BQ.1.1. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 29

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

An SAE was defined as any AE that resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in disability/permanent damage, was a congenital anomaly/birth defect, or was an important medical event. AESIs included thrombocytopenia, new onset of or worsening of the protocol specified neurologic diseases, anaphylaxis, and myocarditis/pericarditis. An MAAE is an AE that lead to an unscheduled visit to a healthcare practitioner. This included visits to a study site for unscheduled assessments (for example, abnormal laboratory follow-up, and/or coronavirus disease 2019 \[COVID-19\] and visits to healthcare practitioners external to the study site (for example, urgent care, primary care physician). Number of participants with SAEs, AESIs, MAAEs, and AEs leading to discontinuation up to the end of study (EOS) are reported in this outcome measure.

Time frame: Day 1 to EOS (Day 366 for Parts A.1, B, C, D, E, and F; and Day 181 for Parts A.2, H, and J)

Population: Safety Set included all participants who received IP.

Solicited ARs (local and systemic) were collected in an electronic diary (eDiary). Local ARs included: injection site pain, injection site erythema (redness), injection site swelling/induration (hardness), and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs included: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. All solicited ARs considered causally related to injection were graded 0-4 (per Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials); lower score indicates lower severity, and a higher score indicates greater severity. The Investigator reviewed whether the solicited AR was also to be recorded as an adverse event (AE). A Summary of serious AEs (SAEs) and nonserious AEs (Other), regardless of causality, is located in the Reported Adverse Events section.

Time frame: 7 days post-vaccination

Population: Solicited Safety Set included all participants who received IP and contributed any solicited AR data.

An AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. Any abnormal laboratory test result (hematology, clinical chemistry, or prothrombin time \[PT\]/partial thromboplastin time \[PTT\]) or other safety assessment (for example, electrocardiogram, radiological scan, vital sign measurement), including one that worsened from baseline and was considered clinically significant in the medical and scientific judgment of the Investigator was recorded as an AE. Number of participants with unsolicited AEs (SAEs and non-serious AEs) up to 28 days post-vaccination are reported in this outcome measure.

Time frame: Up to 28 days post-vaccination

Population: Safety Set included all participants who received IP.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 29 are reported. mRNA-1273.214 (50 μg) as a second booster dose (Part A.2) was compared to mRNA-1273.211 (50 μg) as the first booster dose (Part A.1). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 181 are reported. mRNA-1273.214 (50 μg) as a second booster dose (Part A.2) was compared to mRNA-1273.211 (50 μg) as the first booster dose (Part A.1). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 29 are reported. mRNA-1273.214 (50 μg) as a second booster dose (Part A.2) was compared to mRNA-1273.211 (50 μg) as the first booster dose (Part A.1). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Day 29 are reported. Part F (Cohort 2) mRNA-1273.529 50 μg was compared to Part F (Cohort 2) mRNA-1273 50 μg. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against BA.4/BA.5 and ancestral SARS-CoV-2 (D614G) at Day 29 are reported. mRNA-1273.222 (Part H) was compared to mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) at Day 181 are reported. mRNA-1273.214 (50 μg) as a second booster dose (Part A.2) was compared to mRNA-1273.211 (50 μg) as the first booster dose (Part A.1). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Day 29 are reported. Part F (Cohort 2) mRNA-1273.529 50 μg was compared to Part F (Cohort 2) mRNA-1273 50 μg. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against BA.4/BA.5 and ancestral SARS-CoV-2 (D614G) at Day 29 are reported. mRNA-1273.222 (Part H) was compared to mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against BA.4/BA.5 at Day 15 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 15

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against BA.4/BA.5 at Day 29 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 29

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Day 29 are reported. mRNA-1273.214 (Part G) was compared the mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Day 91 are reported. mRNA-1273.214 (Part G) was compared the mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 91

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against BA.4/BA.5 at Day 15 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 15

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against BA.4/BA.5 at Day 29 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 29

Population: PPIS included all participants who received study injection; had pre-booster and Day 15 nAb data; and who had no major protocol deviations that impacted key or critical data.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Day 29 are reported. mRNA-1273.214 (Part G) was compared the mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Day 91 are reported. mRNA-1273.214 (Part G) was compared the mRNA-1273 (Part F, Cohort 2, 50 μg mRNA-1273). Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Day 91

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure.

GMT of serum pseudovirus nAb ID50 titers against ancestral SARS-CoV-2 (D614G) at Day 181 is reported. 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 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this endpoint.

GMT of serum pseudovirus nAb ID50 titers against ancestral SARS-CoV-2 (D614G) at Day 29 is reported. 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 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

GMT of serum pseudovirus nAb ID50 titers against BA.4/BA.5 at Day 181 is reported. 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 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this endpoint.

GMT of serum pseudovirus nAb ID50 titers against Omicron BA.1 Variant (B.1.1.529) and ancestral SARS-CoV-2 (D614G) on Days 181 and 366 is reported. 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 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Days 181 and 366

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure. 'Number analyzed' = participants evaluable for specified category.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against ancestral SARS-CoV-2 (D614G) at Day 181 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this endpoint.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against BA.4/BA.5 at Day 181 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this endpoint.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against ancestral SARS-CoV-2 (D614G) at Day 181 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this endpoint.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against BA.4/BA.5 at Day 181 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 36.7 AU/mL and ULOQ was 13705 AU/mL for ID50 titer against BA.4/BA.5.

Time frame: Day 181

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this endpoint.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against ancestral SARS-CoV-2 (D614G) at Day 29 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against ancestral SARS-CoV-2 (D614G) on Days 29, 91, 181, and 366 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Days 29, 91, 181, and 366

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Number analyzed' = participants evaluable at specified timepoints.

Percentage of participants with seroresponse (based on the pre-booster baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Days 181 and 366 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Days 181 and 366

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure. 'Number analyzed' = participants evaluable at specified timepoint.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against ancestral SARS-CoV-2 (D614G) at Day 29 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Day 29

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against ancestral SARS-CoV-2 (D614G) on Days 29, 91, 181, and 366 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 18.5 AU/mL and ULOQ was 45118 AU/mL for ID50 titer against ancestral SARS-CoV-2.

Time frame: Days 29, 91, 181, and 366

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Number analyzed' = participants evaluable at specified timepoints.

Percentage of participants with seroresponse (based on the pre-vaccination baseline) for pseudovirus nAb ID50 against Omicron BA.1 Variant (B.1.1.529) at Days 181 and 366 are reported. Seroresponse was defined as a change from below the LLOQ to equal above 4 \* LLOQ, or at least a 4-fold rise if baseline is equal to or above the LLOQ. LLOQ was 19.85 AU/mL and ULOQ was 15502.7 AU/mL for ID50 titer against B.1.1.529.

Time frame: Days 181 and 366

Population: PPIS-Neg included all participants who received study injection; had pre-booster and Day 29 nAb data; had no major protocol deviations that impacted key or critical data; had no previous HIV infection; and who had no serologic or virologic evidence of SARS-CoV-2 infection at baseline. 'Overall number of participants analyzed' = participants evaluable for this outcome measure. 'Number analyzed' = participants evaluable at specified timepoint.