Study to Evaluate the Safety, Reactogenicity, and Effectiveness of mRNA-1273.214 SARS-CoV-2 (COVID-19) Vaccine in Infants

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 were identified based upon medical concepts that may be related to COVID-19 or were of interest in COVID-19 vaccine safety surveillance. MAAE was an AE that led to an unscheduled visit to a healthcare practitioner, included visits to a study site for unscheduled assessments (for example, abnormal laboratory follow-up, and visits to healthcare practitioners external to the study site \[for example, urgent care, primary care physician\]). A summary of SAEs and nonserious AEs (Safety Set), regardless of causality, is located in the AE section. COVID-19/SARS-CoV-2 infections were considered clinical events and not AEs.

Time frame: Day 1 up to Day 422

Population: Safety Set included participants who received at least 1 dose of study drug.

Solicited ARs (local and systemic) were collected in an electronic diary (eDiary). Local ARs included injection site pain/tenderness, injection site erythema (redness), injection site swelling/induration (hardness), and groin or underarm swelling or tenderness ipsilateral to the side of injection. Systemic ARs included fever, irritability/crying, sleepiness, and loss of appetite. Solicited AR severity was graded according to a modified version (relevant to age 12 weeks to \<6 months) of the Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventative Vaccine Clinical Trials. ARs graded 1-4 are presented. Lower scores indicated lower severity, and higher scores indicated greater severity. A summary of serious adverse events (SAEs) and nonserious adverse events (AEs) (Safety Set), regardless of causality, is located in the AE section.

Time frame: Day 1 up to 7 days after first vaccination (up to Day 8)

Population: Solicited Safety Set (First Injection) included participants who received the first injection of study drug and contributed any solicited AR data.

Solicited ARs (local and systemic) were collected in eDiary. Local ARs included injection site pain/tenderness, injection site erythema (redness), injection site swelling/induration (hardness), and groin or underarm swelling or tenderness ipsilateral to the side of injection. Systemic ARs included fever, irritability/crying, sleepiness, and loss of appetite. Solicited AR severity was graded according to a modified version (relevant to age 12 weeks to \<6 months) of the Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventative Vaccine Clinical Trials. ARs graded 1-4 are presented. Lower scores indicated lower severity, and higher scores indicated greater severity. A summary of SAEs and nonserious AEs (Safety Set), regardless of causality, is located in the AE section.

Time frame: Day 57 up to 7 days after second vaccination (up to Day 64)

Population: Solicited Safety Set (Second Injection) included participants who received the second injection of study drug and contributed any solicited AR data.

An unsolicited AE was any AE reported by the participant that was not specified as a solicited AR in the protocol or was specified as a solicited AR but started outside the protocol-defined period for reporting solicited ARs (onset after Day 7 of dosing). 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 or other safety assessment, including one that worsened from baseline and was considered clinically significant by the Investigator was recorded as an AE. A summary of SAEs and nonserious AEs (Safety Set), regardless of causality, is located in the AE section. COVID-19/SARS-CoV-2 infections were considered clinical events and not AEs.

Time frame: Day 1 up to 28 days after any vaccination (up to Day 85)

Population: Safety Set included participants who received at least 1 dose of study drug.

Pseudovirus nAb were measured using pseudovirus neutralization assay (PsVNA). 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. VAC122 nAb against the SARS-CoV-2 B.1.1.529 variant (LLOQ: 8 arbitrary unit (AU)/milliliter (mL), ULOQ: 24503 AU/mL).

Time frame: Baseline and 28 days after second dose (Day 85)

Population: PPIS: participants who received the planned doses of investigational product per schedule, complied with immunogenicity testing schedule, had Baseline (Day 1) and Day 85 antibody assessments, and had no major protocol deviations that impacted key or critical data.

Pseudovirus nAb were measured using PsVNA assay. 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. VAC62 Neutralizing Antibody against D614G (LLOQ: 10 AU/mL, ULOQ: 111433 AU/mL).

Time frame: Baseline and 28 days after second dose (Day 85)

Population: PPIS: participants who received the planned doses of investigational product per schedule, complied with immunogenicity testing schedule, had Baseline (Day 1) and Day 85 antibody assessments, and had no major protocol deviations that impacted key or critical data. Number analyzed = participants evaluable for the specified timepoint.