The change from baseline in FVIII activity, as measured by chromogenic substrate assay, during Weeks 49 to 52 post-BMN 270 infusion. Each subject's FVIII activity level during Week 49 to 52 is defined as the median of the values obtained during week 49-52 with the analysis window defined. Baseline: prior to BMN 270 infusion while receiving FVIII prophylaxis. The baseline value is imputed as 1 IU/dL for each subject.

The change from baseline (assuming no treatment for severe hemophilia A) in FVIII activity, as measured by chromogenic substrate assay (CSA), at Week 52 (during Weeks 49 - 52) post-BMN 270 infusion. Each participant's FVIII activity level at Week 52 is defined as the median of the values obtained within the analysis window at Weeks 49-52. The baseline value will be imputed as 1 IU/dL, since there will be no washout of severe hemophilia A participants' usual FVIII prophylaxis (in order to avoid increasing the risk of bleeding) prior to BMN 270 infusion. Post-BMN 270 infusion values for FVIII activity will be excluded from analysis if obtained within 72 hours (or 3 calendar days if time is not available) since the last infusion of exogenous FVIII replacement therapy. Baseline: prior to BMN 270 infusion while receiving FVIII prophylaxis.

Change of the FVIII activity, as measured by chromogenic substrate assay, at Week 52 post-BMN 270 infusion.

All bleeds comprises both treated and non-treated bleeds. In this definition, all bleeds are included, irrespective of treatment with coagulation factors, with the following exception: bleeds due to surgery/procedure are excluded. All bleeds are any reported bleeding events regardless of the use of FVIII or other treatments. ABR for all bleeds= Number of bleeding episodes for all bleeds during the calculation period / total number of days during the calculation period \* 365.25. Baseline: prior to BMN 270 infusion while receiving FVIII prophylaxis. EEP: From Week 5 post-BMN 270 infusion (Study Day 33) or the end of FVIII prophylaxis plus the washout period (3 days for products of standard half-life or plasma-derived and 5 days for products of extended half-life), whichever is later, to last visit by the data cut-off for the 2-year analysis, hereafter referred to as "Post FVIII Prophylaxis to Last Visit").