Fig. 1

Modelling travellers’ risk when visiting a risk area. The key features to note are that travellers’ exposure varies depending on the time of entry (t _e ) in relation to the start and end of the observation (t  = 0, t  =  t _obs   =  D _o ). Transmission risk is further affected by the time of getting infected (t _i ), and the time of donating (t _x ) after the travellers’ return to their home country. Transmission will only occur if donation takes place within the remaining infectious period (D _x ). Other factors considered are the duration of the visit D _v , the duration of infectivity D _i , and the duration of the observation D _o . Returning donors who have already donated at the end of observation t _obs (past transmissions) can obviously not be prevented. Transmissions that are yet to occur (future transmissions) can be prevented by implementing additional safety interventions