This is a Phase 2, two-part, open-label in Part 1 and observer-blind, randomized, placebo controlled in Part 2 study to evaluate the safety, tolerability, reactogenicity, and effectiveness of mRNA-1273.214 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine in infants aged 12 weeks to < 6 months.

Inclusion Criteria
Participants are eligible to be included in the study only if all the following criteria apply:
1. The participant is male or female, between 2 and < 6 months of age at the time of consent
(Screening Visit), who is in good general health, in the opinion of the investigator, based
on review of medical history and screening physical examination.
a) Participant must be at least 12 weeks completed age and must not have completed
6 months at the time of administration of first dose.
b) If the participant has a chronic, stable disease, they may be eligible to enroll in
Part 2, but ineligible for Part 1. The chronic condition (eg, gastroesophageal
reflux disease) should be stable, per investigator assessment, so that the
participant can be considered eligible for inclusion in Part 2. Note: a change in
medication for dose optimization, change within class of medication, reduction in
dose or increase in dose due to expected weight gain are not considered signs of
instability.
2. The participant was born at ≥ 37 weeks gestation (Part 1) or ≥ 34 weeks gestation
(Part 2), with a minimum birth weight of 2.5 kg, without fetal growth restriction, and the
participant’s height and weight are both at or above the second percentile for age
according to the CDC/WHO Child Growth Standard (Section 11.1.18) at the Screening
Visit.
3. In the investigator’s opinion, the parent(s)/LAR(s) understand and are willing and
physically able to comply with protocol-mandated follow-up, including all procedures,
and provide written informed consent. This includes inability to collect minimum amount
of sample volume at baseline blood draw.

Exclusion Criteria
Participants will be excluded from the study if any of the following criteria apply:
1. The participant has a known history of symptomatic SARS-CoV-2 infection within
2 weeks prior to administration of IP or has a known close contact (as defined in
Section 8.10.2) in the past 2 weeks to someone diagnosed with SARS-CoV-2 infection or COVID-19. Participants may be rescreened after 14 days provided that they remain
asymptomatic.
2. The participant is acutely ill or febrile 72 hours prior to or at the Screening Visit. Fever is
defined as a body temperature ≥ 38.0°C/≥ 100.4°F. Participants who meet this criterion
may have visits rescheduled within the relevant study visit windows. Afebrile participants
with minor illnesses can be enrolled at the discretion of the investigator.
3. The participant has previously been administered an investigational or approved CoV (eg,
SARS-CoV-2, SARS-CoV, MERS-CoV) vaccine.
4. The participant has undergone treatment with investigational or approved agents for
prophylaxis against COVID-19 (eg, receipt of SARS-CoV-2 monoclonal antibodies)
within 90 days prior to enrollment.
5. The participant has a known hypersensitivity to a component of the vaccine or its
excipients. Hypersensitivity includes, but is not limited to, anaphylaxis or immediate
allergic reaction of any severity to any of the components of mRNA COVID-19 vaccines
(including PEG or immediate allergic reaction of any severity to polysorbate).
6. The participant has a medical, psychiatric, or occupational condition, including reported
history of substance abuse, in the infant or in the parent(s)/LAR(s) that, according to the
investigator’s judgment, may pose additional risk as a result of participation, interfere
with safety assessments, or interfere with interpretation of results.
7. The participant has a history of diagnosis or condition that, in the judgment of the
investigator, may affect study endpoint assessment or compromise participant safety,
specifically the following:
a) Congenital or acquired immunodeficiency
b) Chronic hepatitis or suspected active hepatitis
c) A bleeding disorder that is considered a contraindication to IM injection or
phlebotomy, or non-receipt of vitamin K at birth
d) Dermatologic conditions that could affect local solicited AR assessments
e) Any prior diagnosis of malignancy
f) Febrile seizures

The participant has received the following:
a) Any routine vaccination with inactivated or live vaccine(s) within 14 days prior to
first or second vaccination or plans to receive such a vaccine within 14 days of
any study vaccination.
b) Systemic immunosuppressants or immune-modifying drugs (including maternal
use during pregnancy or lactation) for > 14 days in total within 6 months prior to
the day of enrollment (for corticosteroids, ≥ 1 mg/kg/day or, if participant weighs
> 10 kg: ≥ 10 mg/day prednisone equivalent). Participants may have visits
rescheduled for enrollment if they no longer meet this criterion within the
Screening Visit window. Inhaled, nasal, and topical steroids are allowed.
c) Intravenous or subcutaneous blood products (red blood cells, platelets,
immunoglobulins) within 3 months prior to enrollment.
9. The participant has participated in an interventional clinical study within 28 days prior to
the Screening Visit or plans to do so while participating in this study, or maternal
participation in an interventional clinical study during pregnancy.
10. The participant is an immediate family member, or household contact, of an employee of
the study site or Sponsor or someone otherwise directly involved with the conduct of the
study. As applicable, family members/household contacts of employees of the larger
institution or affiliated private practice not part of the study site may be enrolled.
11. The participant is a child who has been placed under the control or protection of an
agency, organization, institution or entity by the courts, the government, or a government
body, acting in accordance with powers conferred on them by laws and regulation. Does
not include a child who is adopted or has an appointed legal guardian.