Implementation considerations ƒ Lack of an appropriate response should be defined as a less than one-third relative reduction in prevalence comparing the baseline prevalence survey and a repeat prevalence survey completed after 2 years of annual preventive chemotherapy. The intervening period should include a minimum of two rounds of preventive chemotherapy to all at-risk groups at adequate treatment coverage (≥ 75%). The relative reduction in prevalence can be estimated as follows: [(prevalence at baseline − prevalence at year 3)/(prevalence at baseline)]. Alternative definitions could consider absolute changes in prevalence of infection, or changes in average intensity of infection (defined as egg concentrations in stool or urine). ƒ The timing of prevalence surveys should consider the seasonality of transmission to ensure that prevalence is measured at the same point in each seasonal transmission cycle. ƒ Communities suspected to be persistent hot spots or of high endemicity (defined as areas with baseline prevalence ≥ 50% in SAC are encouraged to conduct early prevalence surveys (after two annual rounds of preventive chemotherapy) to inform any decision on the use of biannual treatment. ƒ Biannual preventive chemotherapy should be prioritized in areas of higher prevalence (defined as areas with baseline prevalence ≥ 50% in SAC and persistent hot spot settings already achieving high levels of coverage of annual preventive chemotherapy without appropriate response. In settings of moderate prevalence (defined as areas with prevalence 10– 49% in SAC), annual treatment may be sufficient. ƒ Routine monitoring for effective treatment coverage should be an integral part of preventive chemotherapy programmes, with attention to ensuring that annual treatment achieves high coverage (≥ 75%) before any decision to move to biannual treatment. ƒ There is currently a lack of evidence to inform recommendations on the duration of biannual treatment. As an interim measure, 3 consecutive years of biannual preventive chemotherapy is suggested, followed by implementation of an impact survey to assess if it should be continued or reduced in frequency. ƒ Biannual treatment programmes will require a larger global supply of praziquantel than that currently available via donation schemes (estimated at 300 million tablets annually at the time of publication of this guideline). ƒ Biannual treatment programmes should have administrations spaced out equally throughout the year (approximately 6 months between treatments).