The lower sensitivity of 81% for FebriDx MxA compared with PCR may relate to the study including large numbers of frail elderly patients who did not have pneumonia and had low levels of RNA detected, likely representing persistent viral shedding from past infection.23 Although this lower sensitivity resulted in small numbers of patients being moved to a lower-risk area and subsequently testing PCR positive for SARS-CoV-2, these patients likely represent a lower infective risk. Here, MX1 is linked to susceptibility to pneumonia measurement.