NEQAS BC Sheffield

Dear Editors, Historical modifications to FVIII to extend its half-life have been limited by binding to endogenous VWF, initially delivering moderate success as evidenced by around 1.5–1.6-fold half-life extension relative to standard half-life FVIII. More recently a 3–4-fold extension to half-life has been achieved by linking FVIII to the D`D3 region of VWF along with other modifications to circumvent the problem of linkage to native VWF to create efanesoctocog alfa (EFA).

Conflicts of Interest The authors declare no conflicts of interest. Data Availability Statement The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. References 1 and , “The Hemophilias–From Royal Genes to Gene Therapy,” New England Journal of Medicine 344 (2001): 1773–1779.