Perceived risk is influenced by several stimulus characteristics, including unfamiliarity, invisibility, dreadfulness and inequity [32] , and by recipient characteristics, including demographics and trust in information source and content [33] . Perceived risk is an important determinant of protective behavioural responses [12, 34, 35, 36] , but is subject to optimistic bias, where for example people distort their risk of contracting influenza downwards relative to others [35, 37] . Nonetheless, susceptibility to risk remains an important measure in understanding variation in behavioural responses to threat and reflects the key element of perceived risk in an epidemic/pandemic situation. Worry is a cognitive process linked to anxiety [26, 38] and reflects negative affectivity, interacting with perception of susceptibility to risk [26, 39] and may also influence RID protective responses such as social distancing [13] .