An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of study intervention. An SAE was defined as any untoward medical occurrence that, at any dose, met one or more of the criteria as follows: death, life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, congenital anomaly/birth defect and other situations per protocol. AEs included both SAEs and all non-SAEs.

Safety population included all participants enrolled in this study who received any portion of study intervention.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by chromogenic assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the Statistical Analysis Plan (SAP).

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by chromogenic assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by chromogenic assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by chromogenic assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by chromogenic assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by one-stage clotting assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by one-stage clotting assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by one-stage clotting assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by one-stage clotting assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were assessed using chromogenic and one-stage clotting assay and which were analyzed in the central laboratory. In this outcome measure results by one-stage clotting assay are reported.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure. For Cohort 1, both participants resumed prophylaxis regimen prior to Week 52, and were excluded from analysis as pre-specified in the SAP.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by chromogenic assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 1 included assessments from Week 9 through Week 53). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the statistical analysis plan (SAP) of the study, this outcome measure was to be assessed only in Cohort 4.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by chromogenic assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 2 included assessments from Week 54 through Week 108). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by chromogenic assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 3 included assessments from Week 109 through Week 160). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by chromogenic assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 4 included assessments from Week 161 through Week 212). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by chromogenic assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 5 included assessments from Week 213 through Week 264). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by one-stage clotting assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 1 included assessments from Week 9 through Week 53). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by one-stage clotting assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 2 included assessments from Week 54 through Week 108). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by one-stage clotting assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 3 included assessments from Week 109 through Week 160). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by one-stage clotting assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 4 included assessments from Week 161 through Week 212). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure.

FVIII activity levels were analyzed in the central laboratory using chromogenic and one-stage clotting assay. In this outcome measure FVIII activity levels were assessed by one-stage clotting assay. As pre-specified, for each participant geometric mean of central FVIII activity levels was calculated of all eligible FVIII activity measurements for each yearly interval (for this outcome measure: Yearly Interval 5 included assessments from Week 213 through Week 264). Following this mean and standard deviation as summary statistics across all evaluable participants was calculated and is reported as data for this outcome measure.

Safety population included all participants enrolled in this study who received any portion of study intervention. As pre-specified in planned analysis in the SAP of the study, this outcome measure was to be assessed only in Cohort 4. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure.

Total ABR included both treated and untreated bleeding episodes. In this outcome measure total ABR for pre-screening and post-infusion are reported. Pre-screening total ABR was based on the total number of reported bleeding episodes during 12 months prior to screening visit as reported on CRF's Hemophilia A History page. Screening was 2 months before baseline. Post- infusion total ABR = number of all bleeding episodes starting 3 weeks after investigational product/ PF-07055480 (IP) infusion up to date of day before start of prophylaxis (or date of data cut or conclusion date)/ observation period in years, where observation period in years = date of day before start of prophylaxis or date of data cut or conclusion date - 3 weeks after date of IP infusion + 1)/365.25. For a participant who did not start prophylaxis the data cut date or conclusion date is used.

Safety population included all participants enrolled in this study who received any portion of study intervention.

Total ABR include both treated and untreated bleeding episodes. In this outcome measure total ABR by severity for post-infusion period is reported. Severity was categorized as mild, moderate and severe. Post- infusion total ABR = number of all bleeding episodes starting 3 weeks after IP infusion up to date of day before start of prophylaxis (or date of data cut or conclusion date)/ observation period in years, where observation period in years = date of day before start of prophylaxis or date of data cut or conclusion date - 3 weeks after date of IP infusion + 1)/365.25. For a participant who did not start prophylaxis the data cut date or conclusion date is used.

Safety population included all participants enrolled in this study who received any portion of study intervention.

AIR was calculated and reported for pre-infusion and post-infusion. AIR for pre-infusion was calculated as, a) Excluding prophylaxis: number of FVIII replacement infusions for reasons other than prophylaxis prior to IP infusion/ ([date of IP infusion - date of screening] + 30)] *365.25, or b) number of FVIII replacement infusions for any reason prior to IP infusion/ ([date of IP infusion - date of screening] + 30)] *365.25. Screening was 2 months before baseline and baseline was approximately 1-week prior to IP infusion. AIR for post- infusion was calculated as: number of FVIII replacement infusions started at 3 weeks after IP infusion up to date of data cut or conclusion date/ number of days in the observation period for the participant in years, where observation period in years = date of data cut or conclusion date - 3 weeks after date of IP infusion + 1)/365.25.

Safety population included all participants enrolled in this study who received any portion of study intervention.

EQ-5D-5L is a standardized measure of health status developed by the EuroQol Group. It measures 5 dimensions (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression) of health on a 5-point scale. Each dimension had 5 levels: 1= no problems, 2= slight problems, 3= moderate problems, 4= severe problems, and 5= extreme problems. EQ-5D-5L had 2 components: Index score and visual analogue scale (VAS). Index score was obtained, according to the health state defined by the 5 dimensions scores, from the Crosswalk Index value calculator and table lookup document under the target country population. A health state is defined by the combination of one level from each of the 5 dimensions. For this study, weights under the US population were used to obtain the Index score. Index score ranged between 0-1, where higher score indicates a better health state, and lower score indicate worse health state. Baseline was defined as the latest non-missing value before IP infusion.

Safety population. Here, "Number Analyzed" =participants evaluable for specified timepoints. Participants from "Cohort 1: PF-07055480 9*10^11 vg/kg" and "Cohort 2: PF-07055480 2*10^12 vg/kg" did not attend the study visit or missed the EQ-5D-5L assessment at Months 24 and 60 and participants from "Cohort 3: PF-07055480 1*10^13 vg/kg" did not attend the study visit or missed the EQ-5D-5L assessment at Month 24; hence, no participants were analyzed for Cohorts 1, 2 and 3 at the mentioned visits.

EQ-5D-5L is a standardized measure of health status developed by the EuroQol Group. It measures 5 dimensions of health on a 5-point scale including mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Each dimension is assessed with 5 levels: 1= no problems, 2= slight problems, 3= moderate problems, 4= severe problems, and 5= extreme problems. EQ-5D-5L had 2 components: Index score and VAS. EQ-5D-5L VAS: Participants were asked to indicate their current health status on a scale of 0 (worst health) to 100 (best imaginable health), higher scores signified better health status. Baseline was defined as the latest non-missing value before IP infusion.

Safety population. Here, "Number Analyzed" =participants evaluable for specified timepoints. Participants from "Cohort 1: PF-07055480 9*10^11 vg/kg" and "Cohort 2: PF-07055480 2*10^12 vg/kg" did not attend the study visit or missed the EQ-5D-5L assessment at Months 24 and 60 and participants from "Cohort 3: PF-07055480 1*10^13 vg/kg" did not attend the study visit or missed the EQ-5D-5L assessment at Month 24; hence, no participants were analyzed for Cohorts 1, 2 and 3 at the mentioned visits.

Positive FVIII inhibitor was assessed using central laboratory using Nijmegen method of the Bethesda assay in an individual with no prior history of FVIII inhibitor. Inhibitor assay results >0.6 Bethesda units (BU) were considered as positive. Positive results at any timepoint were considered, even if subsequent inhibitor assessment was negative.

Safety population included all participants enrolled in this study who received any portion of study intervention.

Peak (maximum) AAV2/6 vector DNA concentration (vg/mL) in plasma, saliva, semen, stool and urine were analyzed with quantitative real-time polymerase chain reaction (PCR). Participants must achieve 3 consecutive negative results for analysis for each sample.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Number Analyzed" signifies participants evaluable for the specified rows.

Time to peak (maximum) AAV2/6 vector DNA concentration (vg/mL) in plasma, saliva, urine, stool and semen were analyzed with quantitative real-time PCR. Participants must achieve 3 consecutive negative results for analysis for each sample; where negative suggests values under the limit of detection.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Number Analyzed" signifies participants evaluable for the specified rows.

Time to undetectable (negative) value of AAV2/6 vector DNA concentration (vg/mL) in plasma, saliva, urine, stool and semen were analyzed with quantitative real-time PCR. Time to undetectable is defined as the number of days from IP infusion until the first of 3 consecutive specimens under the limit of detection (negative).

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Number Analyzed" signifies participants evaluable for the specified rows.

Time to last of 3 consecutive negative value of AAV2/6 vector DNA concentration (vg/mL) in plasma, saliva, urine, stool and semen were analyzed with quantitative real-time PCR.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Number Analyzed" signifies participants evaluable for the specified rows.

Time to last positive value prior to first of 3 consecutive negatives of AAV2/6 vector DNA concentration (vg/mL) in plasma, saliva, urine, stool and semen were analyzed with quantitative real-time PCR, where positive suggests values above the limit of detection.

Safety population included all participants enrolled in this study who received any portion of study intervention. Here, "Number Analyzed" signifies participants evaluable for the specified rows.