Seasonal influenza is one of the principal causes of vaccine-preventable disease with up to 500,000 deaths per year worldwide (Thompson et al., 2003). Annual influenza vaccination is the most effective method for preventing influenza virus infection and its complications (Cox and Subbarao, 1999) and has been reported to prevent influenza-related respiratory tract infection by 56%, pneumonia by 53%, hospitalization by 50%, and mortality by 68% (Gross et al., 1995). Unvaccinated health care workers (HCWs) are the main source of nosocomial influenza (Maltezou and Drancourt, 2003) with health care personnel being responsible for up to 50% cases of acute respiratory illness recorded within the hospital during an influenza season in Japan (Kawana et al., 2006). HCWs may be infected in their workplace or may continue working while they are ill (Weingarten et al., 1989). Transmission of influenza from patients to HCWs (Kapila et al., 1977) from HCWs to patients (CDC, 1988) and amongst HCWs (Horman et al., 1986; CDC, 1992) has been plentifully documented in the medical literature. The possible consequences of infected HCWs include increased morbidity and mortality amongst patients at risk for contracting influenza and a high rate of ‘sickness-absenteeism’ amongst the workers themselves resulting in shortage of staff, additional cost to the health care sector and a general taxing of the health care delivery. Sickness absenteeism singly reaches proportions of 30-40% (Hammond and Cheang, 1984; Hansen et al., 2007; Sartor et al., 2002) during influenza outbreaks resulting in a severe compromise in functioning of the health care delivery system. Unvaccinated HCWs, paradoxically transmit influenza through asymptomatic shedding and by the cultural pressure to present for work when ill (‘presentee-ism’) (Tosh et al., 2009). Influenza vaccination of HCWs has been associated with reduced work absenteeism (Elder et al., 1993) and with fewer deaths among nursing home patients (Carman et al., 2000; Potter et al., 1997; Hayward et al., 2006) and elderly hospitalized patients (Thomas et al., 2006). Given the annual burden of nosocomial influenza as well as the benefits of HCW vaccination, the Center for Disease Control and Prevention, (CDC, USA) has recommended influenza vaccination of HCWs since 1960s and the current guidelines for influenza vaccination recommend routine vaccination for all HCWs (CDC, 2010). In times of vaccine shortage they constitute the most important group to whom vaccinations must be administered. The rationale of annual vaccination of HCWs is to limit the exposure to influenza of elderly persons and high risk patients, as they are the ones to use the health care system most frequently and their vaccination has limited effect. Vaccination is recommended for all personnel employed in health-care facilities with or without a health-care occupation, including permanent, casual and contract staff (Russel and Henderson, 2003).