Local reactions included redness, swelling and pain at injection site, recorded by participants in an electronic diary (e-diary). Severity of all local reactions were evaluated as mild, moderate, severe or potentially life-threatening. In this outcome measure local reactions with any severity were reported for each left arm's deltoid and right arm's deltoid of each vaccine Group 1, 2, 3 and 4.

Systemic events: fever, fatigue, headache, vomiting, diarrhea, chills, new/worsened muscle pain, new/worsened joint pain were recorded by participants in e-diary. Severity of all systemic events were evaluated as mild, moderate, severe or potentially life-threatening. In this outcome measure systemic events with any severity were reported.

An AE was defined as any untoward medical occurrence in a participant temporally associated with the use of study intervention, whether or not considered related to the study intervention. Events collected by systematic assessment (local reactions and systemic events) were excluded from evaluation.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An SAE was defined as any untoward medical occurrence that, at any dose, met one or more of the following criteria - resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect and other important medical events per protocol of the study. Events collected by systematic assessment (local reactions and systemic events) were excluded from evaluation.

GMTs and the corresponding 2-sided CIs were calculated by exponentiating the mean logarithm of the titers and the corresponding CIs (based on the Student t distribution). As planned, outcome measure evaluated GMTs of SARS-CoV-2 Omicron (XBB.1.5), hence results are reported only for those reporting groups where BNT162b2 (Omi XBB.1.5) was administered. Data was not collected and not reported for reporting group "Group 4: RIV + Placebo", where BNT162b2 (Omi XBB.1.5) was not administered.

GMTs and the corresponding 2-sided CIs were calculated by exponentiating the mean logarithm of the titers and the corresponding CIs (based on the Student t distribution). As planned, outcome measure evaluated GMTs of SARS-CoV-2 Omicron (XBB.1.5), hence results are reported only for those reporting groups where BNT162b2 (Omi XBB.1.5) was administered. Data was not collected and not reported for reporting group "Group 4: RIV + Placebo", where BNT162b2 (Omi XBB.1.5) was not administered.

GMFR was the ratio of the geometric mean titre values 4 weeks after vaccination to before vaccination. GMFRs and the corresponding 2-sided CIs were calculated by exponentiating the mean logarithm of fold rises and the corresponding CIs (based on the Student t distribution). As planned, outcome measure evaluated GMTs of SARS-CoV-2 Omicron (XBB.1.5), hence results are reported only for those reporting groups where BNT162b2 (Omi XBB.1.5) was administered. Data was not collected and not reported for reporting group "Group 4: RIV + Placebo", where BNT162b2 (Omi XBB.1.5) was not administered.

Seroresponse was defined as achieving a \>=4-fold rise from baseline (before the study vaccination). If the baseline measurement was below the lower limit of quantification (LLOQ), the postvaccination measure of \>=4\*LLOQ is considered a seroresponse. Exact 2-sided CI, based on the Clopper and Pearson method. As planned, outcome measure evaluated GMTs of SARS-CoV-2 Omicron (XBB.1.5), hence results are reported only for those reporting groups where BNT162b2 (Omi XBB.1.5) was administered. Data was not collected and not reported for reporting group "Group 4: RIV + Placebo", where BNT162b2 (Omi XBB.1.5) was not administered.

GMTs and the corresponding 2-sided CIs were calculated by exponentiating the mean logarithm of the titers and the corresponding CIs (based on the Student t distribution). The 4 virus strains which were evaluated and reported in this outcome measure were A/Victoria/4897/2022 (H1N1) HAI, A/Darwin/9/2021 (H3N2) HAI, B/Michigan/1/2021 HAI and B/Phuket/3073/2013 HAI. As planned, outcome measure evaluated GMTs of strain specific HAI, hence results are reported only for those reporting groups where RIV was administered. Data was not collected and not reported for reporting group "Group 3: BNT162b2 (Omi XBB.1.5) + Placebo", where RIV was not administered.

GMTs and the corresponding 2-sided CIs were calculated by exponentiating the mean logarithm of the titers and the corresponding CIs (based on the Student t distribution). The 4 virus strains which were evaluated and reported in this outcome measure were A/Victoria/4897/2022 (H1N1) HAI, A/Darwin/9/2021 (H3N2) HAI, B/Michigan/1/2021 HAI and B/Phuket/3073/2013 HAI. As planned, outcome measure evaluated GMTs of strain specific HAI, hence results are reported only for those reporting groups where RIV was administered. Data was not collected and not reported for reporting group "Group 3: BNT162b2 (Omi XBB.1.5) + Placebo", where RIV was not administered.

GMFR was the ratio of the geometric mean titre values 4 weeks after vaccination to before vaccination. GMFRs and the corresponding 2-sided CIs were calculated by exponentiating the mean logarithm of fold rises and the corresponding CIs (based on the Student t distribution). The 4 virus strains which were evaluated and reported in this outcome measure were A/Victoria/4897/2022 (H1N1) HAI, A/Darwin/9/2021 (H3N2) HAI, B/Michigan/1/2021 HAI and B/Phuket/3073/2013 HAI. As planned, outcome measure evaluated GMFRs of strain specific HAI, hence results are reported only for those reporting groups where RIV was administered. Data was not collected and not reported for reporting group "Group 3: BNT162b2 (Omi XBB.1.5) + Placebo", where RIV was not administered.

Seroconversion was defined as an HAI titer \<1:10 prior to vaccination and \>=1:40 at the time point of interest, or an HAI titer of \>=1:10 prior to vaccination with a minimum 4-fold rise at the time point of interest. Exact 2-sided CI, based on the Clopper and Pearson method. The 4 virus strains which were evaluated and reported in this outcome measure were A/Victoria/4897/2022 (H1N1) HAI, A/Darwin/9/2021 (H3N2) HAI, B/Michigan/1/2021 HAI and B/Phuket/3073/2013 HAI. As planned, outcome measure evaluated seroconversion of strain specific HAI, hence results are reported only for those reporting groups where RIV was administered. Data was not collected and not reported for reporting group "Group 3: BNT162b2 (Omi XBB.1.5) + Placebo", where RIV was not administered.

Percentages of participants with HAI titers \>= 1:40 before vaccination along with the associated 2-sided 95% CIs, was provided for each vaccine group in this outcome measure. Exact 2-sided CI, based on the Clopper and Pearson method. The 4 virus strains which were evaluated and reported in this outcome measure were A/Victoria/4897/2022 (H1N1) HAI, A/Darwin/9/2021 (H3N2) HAI, B/Michigan/1/2021 HAI and B/Phuket/3073/2013 HAI. As planned, outcome measure evaluated of strain specific HAI, hence results are reported only for those reporting groups where RIV was administered. Data was not collected and not reported for reporting group "Group 3: BNT162b2 (Omi XBB.1.5) + Placebo", where RIV was not administered.

Percentages of participants with HAI titers \>= 1:40 at 4 weeks after vaccination along with the associated 2-sided 95% CIs, was provided for each vaccine group in this outcome measure. Exact 2-sided CI, based on the Clopper and Pearson method. The 4 virus strains which were evaluated and reported in this outcome measure were A/Victoria/4897/2022 (H1N1) HAI, A/Darwin/9/2021 (H3N2) HAI, B/Michigan/1/2021 HAI and B/Phuket/3073/2013 HAI. As outcome measure evaluated of strain specific HAI, hence results are reported only for those reporting groups where RIV was administered. Data was not collected and not reported for reporting group "Group 3: BNT162b2 (Omi XBB.1.5) + Placebo", where RIV was not administered.