A Study of mRNA-1020 and mRNA-1030 Seasonal Influenza Vaccines in Healthy Adults

Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)

Solicited ARs (local and systemic) were collected in the electronic diary (eDiary). Local ARs included: pain at injection site, erythema (redness) at injection site, swelling/induration (hardness) at injection site, and localized axillary swelling or tenderness ipsilateral to the injection arm. Systemic ARs included: headache, fatigue, myalgia (muscle aches all over the body), arthralgia (aching in several joints), nausea/vomiting, rash, body temperature (potentially fever), and chills. Note, not all solicited ARs were considered adverse events (AEs). The 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 and presented by each dose group separately.

Time frame: Up to Day 7 (7 days after vaccination)

Number of Participants With Unsolicited Adverse Events (AEs)

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 treatment-emergent AE (TEAE) was defined as any event not present before exposure to vaccine or any event already present that worsens in intensity or frequency after exposure. 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 worsens from baseline and is considered clinically significant in the medical and scientific judgment of the Investigator. A summary of SAEs and all nonserious AEs ("Other") reported up to the end of the study, regardless of causality, is located in the "Reported Adverse Events" section and presented by each dose group separately.

Time frame: Up to Day 28 (28 days after vaccination)

Number of Participants With Medically-Attended AEs (MAAEs), Adverse Event of Special Interest (AESI), AEs Leading to Withdrawal and Serious Adverse Events (SAEs)

An SAE was defined as any AE that resulted in death, is 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 leads to an unscheduled visit to an healthcare practitioner. This would include visits to a study site for unscheduled assessments (for example, abnormal laboratory follow-up, and/or COVID-19 and visits to healthcare practitioners external to the study site (for example, urgent care, primary care physician). A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section and presented by each dose group separately.