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, that 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 all serious AEs (SAEs) and all nonserious AEs ("Other"), regardless of causality, is in Reported "Adverse Events" section.

The solicited safety set consisted of all participants in the safety set who contributed any solicited AR data.

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.

The safety set consisted of all randomly assigned participants who received the IP.

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 a 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.

The safety set consisted of all randomly assigned participants who received the IP.

Seasonal influenza A included H1N1 and H3N2 and seasonal influenza B strains included BV and BY.

Per protocol set consisted of all participants in the FAS who comply with injection schedule, comply with timings of immunogenicity blood sampling to have a baseline and at least 1 post-injection assessment and a Day 29 assessment, do not have influenza or SARS-CoV-2 infection at baseline and post-baseline up to Day 29 and have no major protocol deviations and/or prohibited concomitant medication use that are prespecified with impacts on immune response. N=number evaluable for this endpoint.

Per protocol set consisted of all participants in the FAS who comply with injection schedule, comply with timings of immunogenicity blood sampling to have a baseline and at least 1 post-injection assessment and a Day 29 assessment, do not have influenza or SARS-CoV-2 infection at baseline and post-baseline up to Day 29 and have no major protocol deviations and/or prohibited concomitant medication use that are prespecified with impacts on immune response. N=number evaluable for this endpoint.

Seasonal influenza A included H1N1 and H3N2 and seasonal influenza B strains included BV and BY.

Per protocol set consisted of all participants in the FAS who comply with injection schedule, comply with timings of immunogenicity blood sampling to have a baseline and at least 1 post-injection assessment and a Day 29 assessment, do not have influenza or SARS-CoV-2 infection at baseline and post-baseline up to Day 29 and have no major protocol deviations and/or prohibited concomitant medication use that are prespecified with impacts on immune response. N=number evaluable for this endpoint.

The GMFR measures the changes in immunogenicity titers or levels from Baseline within participants. 95% CI was calculated based on the difference in the log-transformed values for GMFR, then back transformed to the original scale for presentation.

Per protocol set consisted of all participants in the FAS who comply with injection schedule, comply with timings of immunogenicity blood sampling to have a baseline and at least 1 post-injection assessment and a Day 29 assessment, do not have influenza or SARS-CoV-2 infection at baseline and post-baseline up to Day 29 and have no major protocol deviations and/or prohibited concomitant medication use that are prespecified with impacts on immune response. N=number evaluable for this endpoint.

Seroconversion at a participant level is defined as a pre-vaccination HAI titer < 1:10 and a post-vaccination HAI titer >= 1:40 or a pre-vaccination HAI titer >= 1:10 and a minimum 4-fold rise in post vaccination HAI antibody titer.

Per protocol set consisted of all participants in the FAS who comply with injection schedule, comply with timings of immunogenicity blood sampling to have a baseline and at least 1 post-injection assessment and a Day 29 assessment, do not have influenza or SARS-CoV-2 infection at baseline and post-baseline up to Day 29 and have no major protocol deviations and/or prohibited concomitant medication use that are prespecified with impacts on immune response. N=number evaluable for this endpoint.

Seroresponse at a participant level is defined as an increase from below the lower limit of quantification (LLOQ) to >= 4 x LLOQ if baseline neutralizing antibody (nAb) level is < LLOQ, or >= 4 fold rise if baseline nAb level is >=LLOQ.

Per protocol set consisted of all participants in the FAS who comply with injection schedule, comply with timings of immunogenicity blood sampling to have a baseline and at least 1 post-injection assessment and a Day 29 assessment, do not have influenza or SARS-CoV-2 infection at baseline and post-baseline up to Day 29 and have no major protocol deviations and/or prohibited concomitant medication use that are prespecified with impacts on immune response. N=number evaluable for this endpoint.