After the de-duplication process to remove similar sources of evidence, 2993 studies were screened by title and abstract for eligibility, and 2303 of these were excluded, leaving 690 sources to be reviewed by full text for further evaluation; 353 of them were excluded. The remaining 337 studies underwent content evaluation; 312 of these studies were excluded, resulting in 25 studies that met the inclusion criteria for this scoping review (Fig. 2). More details are provided in (Supplementary Methods 3, see ESM).

PRISMA flow chart [27, 28, 160, 161]

Overall, 25 studies enrolling 7226 PwH were included, representing all haemophilia types, severities, and immunogenic statuses, from 22 countries, including six LMICs (Supplementary Table 1, see ESM) [49]. This review included studies published from 1979 to 2023 [50, 51]. For individual studies, the time frame ranged from 6 months [52,53,54] to 11 years [55], and the population size ranged from six [56] to 1285 [57] PwH. Fourteen studies included data from a single country [50, 52, 54, 56, 58,59,60,61,62,63,64,65,66,67]; whereas 11 encompassed multiple countries [47, 51, 53, 55, 57, 68,69,70,71,72,73]. Nine of these studies were conducted in Europe [51, 53, 55, 57, 68, 69, 71,72,73] (Table 1 and Supplementary Table 1, see ESM).

Seventeen studies included people with HA and HB with or without inhibitors [52, 53, 55,56,57,58,59,60,61,62, 65, 66, 68,69,70, 72, 73]; five studies included only those with HA [47, 50, 51, 54, 63], and three included only those with HB [64, 67, 71]. Sixteen studies enrolled PwH without inhibitors [47, 50,51,52, 54, 55, 57,58,59, 65,66,67,68, 71,72,73], whereas eight studies enrolled PwH with or without inhibitors [53, 60,61,62,63,64, 69, 70], and one study enrolled only persons with inhibitors [56]. Twelve studies enrolled PwH in all age groups [47, 50, 51, 54, 55, 60, 61, 63, 64, 66, 69, 70]; eight studies enrolled only adults [52, 57,58,59, 65, 67, 71, 73], three studies enrolled children and adolescents [56, 62, 72]; and two studies enrolled adolescents and adults [53, 68] (Table 1 and Supplementary Table 2, see ESM).

Most of the included studies (76%) were retrospective cross-sectional studies [50,51,52,