mRNA Seasonal Flu vaccine

First occurrence of laboratory-confirmed protocol-defined ILI caused by influenza A subtypes and B lineage. Protocol-defined ILI is defined as the simultaneous occurrence of at least 1 respiratory symptom and at least 1 systemic symptom. Respiratory symptoms include nasal congestion, sore throat, new or increased sputum, new or increased cough, new or increased dyspnea, or wheezing. Systemic symptoms include temperature \>37.2°C/99°F or feverishness, fatigue, myalgia, or headache. The endpoint will be assessed using an incidence rate approach. Relative vaccine efficacy will be calculated as 100 × (1 - incidence rate ratio).

The solicited administration site AEs considered are pain, redness, swelling and lymphadenopathy. Lymphadenopathy is defined as localized axillary, cervical or supraclavicular swelling or tenderness ipsilateral to the injection arm.

The solicited systemic AEs considered are fever, headache, fatigue, myalgia, arthralgia and chills. Fever is defined as temperature greater than or equal to (\>=) 38 °C/100.4 °F regardless the location of measurement.

An unsolicited AE is an AE that was either not included in the list of solicited events or could be included in the list of solicited events but with an onset outside the specified period of follow-up for solicited events.

SAE is an AE which results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in disability/incapacity, or other situations that are considered serious per medical or scientific judgment.

An adverse event of special interest is an adverse event of scientific and medical concern specific to the sponsor's product or program, for which ongoing monitoring and rapid communication by the investigator to the sponsor may be appropriate. AESIs include protocol-defined events such as potential immune-mediated disorders, myocarditis, pericarditis, severe hypersensitivity reactions, and other AESIs defined in the protocol.