Of the 250 healthcare workers, 41 (16%) were doctors, 97 (39%) were trainee nurses and 112 (45%) were qualified nurses. Of the 486 non-healthcare workers, 178 (36%) were administrative or information technology staff, 107 (22%) scientific staff, 45 (9%) students, 6 (1%) teaching or lecturing staff, 25 (5%) in manual or technical roles, 21 (4%) in retail or service, 9 (2%) veterinary staff, and 7 (1%) in other occupations. In 88/486 (18%) the occupation was not stated or unclear. Table 1 compares study characteristics in the exposure group (HCW) and control group (non-HCW). HCWs were significantly younger than controls (35.7 versus 39.2, Kruskal-Wallis test, p < 0.01). They were also significantly more likely to be current smokers, female, vaccinated in the current season, and to own a car.