Geometric Mean Ratio (GMR) Based on Geometric Mean Concentration (GMC) of Full-Length S-binding Immunoglobulin G (IgG) at 1 Month After BNT162b2 Vaccination;Geometric Mean Ratio (GMR) Based on Geometric Mean Titer (GMT) of Strain-Specific Hemagglutination Inhibition (HAI) at 1 Month After SIIV Vaccination;Percentage of Participants With Adverse Events Within 1 Month After Vaccination 1;Percentage of Participants With Adverse Events Within 1 Month After Vaccination 2;Percentage of Participants With Local Reactions Within 7 Days After Vaccination 1;Percentage of Participants With Local Reactions Within 7 Days After Vaccination 2;Percentage of Participants With Serious Adverse Events Within 1 Month After Vaccination 1;Percentage of Participants With Serious Adverse Events Within 1 Month After Vaccination 2;Percentage of Participants With Systemic Events Within 7 Days After Vaccination 1;Percentage of Participants With Systemic Events Within 7 Days After Vaccination 2

Geometric Mean Ratio (GMR) Based on Geometric Mean Concentration (GMC) of Full-Length S-binding Immunoglobulin G (IgG) at 1 Month After BNT162b2 Vaccination;Geometric Mean Ratio (GMR) Based on Geometric Mean Titer (GMT) of Strain-Specific Hemagglutination Inhibition (HAI) at 1 Month After SIIV Vaccination;Percentage of Participants With Adverse Events Within 1 Month After Vaccination 1;Percentage of Participants With Adverse Events Within 1 Month After Vaccination 2;Percentage of Participants With Local Reactions Within 7 Days After Vaccination 1;Percentage of Participants With Local Reactions Within 7 Days After Vaccination 2;Percentage of Participants With Serious Adverse Events Within 1 Month After Vaccination 1;Percentage of Participants With Serious Adverse Events Within 1 Month After Vaccination 2;Percentage of Participants With Systemic Events Within 7 Days After Vaccination 1;Percentage of Participants With Systemic Events Within 7 Days After Vaccination 2

Adverse Events;Full-length S-binding IgG levels;Local reactions (redness, swelling, and pain at the injection site) self-reported on e-diaries;Serious Adverse Events;Strain-specific HAI titers ; H3N2-neutralizing antibody titers (if H3N2-HAI titers cannot be obtained);Systemic events (fever, fatigue, headache, chills, vomiting, diarrhea, new or worsened muscle pain, and new or worsened joint pain) self-reported on e-diaries

Adverse Events;Full-length S-binding IgG levels;Local reactions (redness, swelling, and pain at the injection site) self-reported on e-diaries;Serious Adverse Events;Strain-specific HAI titers ; H3N2-neutralizing antibody titers (if H3N2-HAI titers cannot be obtained);Systemic events (fever, fatigue, headache, chills, vomiting, diarrhea, new or worsened muscle pain, and new or worsened joint pain) self-reported on e-diaries