A Study of Zika Vaccine mRNA-1893 in Adult Participants Living in Endemic and Non-Endemic Flavivirus Areas

This clinical study will evaluate the safety, tolerability, and reactogenicity of 2 dose levels of messenger RNA (mRNA)-1893 Zika vaccine in comparison to a placebo control in healthy participants who are flavivirus-seronegative and in participants who are flavivirus-seropositive.


Eligibility Criteria:
Key Inclusion Criteria:

* Understands and agrees to comply with the study procedures and provides written informed consent.
* According to investigator assessment, is in good general health and can comply with study procedures.
* Female participants of childbearing potential may be enrolled in the study if the participant: has a negative pregnancy test at the Eligibility Visit and on the day of the first investigational product (IP) injection; has practiced adequate contraception or has abstained from all activities that could result in pregnancy for at least 28 days prior to the first IP injection; has agreed to continue adequate contraception through 3 months following the last IP injection; and is not currently breastfeeding.

Key Exclusion Criteria:

* Participant is acutely ill or febrile (temperature ≥38.0°Celsius/100.4°Farenheight) on the day of the first or second vaccination.
* Participant had prior administration of a ZIKV vaccine candidate during a clinical study investigation.
* Participant had prior administration of a marketed dengue vaccine or dengue vaccine candidate under clinical study investigation.
* Participant has a body mass index (BMI) from ≤18 or ≥35 kilograms (kg)/square meter (m\^2).
* Participant has a history of myocarditis, pericarditis, or myopericarditis.
* Participant has a history of a diagnosis or condition that, in the judgement of the investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. "Clinically unstable" is defined as a diagnosis or condition requiring significant changes in management or medication within the 2 months prior to screening and includes ongoing work-up of an undiagnosed illness that could lead to a new diagnosis or condition.
* Participant has any medical, psychiatric, or occupational condition, including reported history of drug or alcohol abuse, that in the opinion of the investigator, might pose a risk due to participation in the study or could interfere with the interpretation of study results.
* Participant has as a history of anaphylaxis, urticaria, or other significant AR requiring medical intervention after receipt of a vaccine, including an mRNA vaccine or any components of an mRNA vaccine.
* Participant has received or plans to receive a nonstudy vaccine (including authorized or approved vaccines for the prevention of COVID-19) ≤28 days prior to the first IP injection or within 28 days prior to or after any IP injection. Licensed influenza vaccine received within 14 days prior to the first IP injection or plans to receive a licensed influenza vaccine 14 days prior to through 14 days following each IP injection are not exclusionary.
* Participant has received systemic immunoglobulins or blood products within 3 months prior to the day of enrollment.
* Participant has donated ≥450 milliliters (mL) of blood products within 28 days of the Day 1 Visit.
* Participant has participated in an interventional clinical study within 28 days prior to the day of enrollment or plans to do so while enrolled in this study.