OBJECTIVES: Typically, healthy adults are not targeted for influenza vaccination, leading to out-of-pocket expenses if they choose to be vaccinated. This can be a deterrent to vaccination coupled with a low concern for consequences of infection. However, despite a lower attack and complication rate than other age/risk groups, infection in healthy employees can result in important loss of productivity to employers. We estimated the benefits of vaccinating healthy employees with a quadrivalent inactivated influenza vaccine (QIV). METHODS: A decision tree model was developed to evaluate an annual employer-paid vaccination program for working adults in the UK versus no vaccination. Probabilities and costs were from peer-reviewed literature and government reports. A population of 5,000 healthy employees, a 75% vaccination coverage and an average daily productivity of two times the average UK wage were assumed. Vaccine efficacy estimates were based on systematic reviews/meta-analyses and a 10-year history of match/mismatch.  Sensitivity analysis of uncertainty was conducted. RESULTS: The model estimated that vaccination with QIV would avert 159 cases of influenza, and 1,066 days of absenteeism, resulting in a productivity loss of £134,007 annually. Considering the vaccine and administration costs (£57,675) the employer would save £76,332. The results are highly sensitive to the number of days an employee is absent due to a simple infection (no hospitalisation), the attack rate, and average productivity. In scenario analysis if the average productivity is set simply to the average wage, the employer would still save £9,328. CONCLUSIONS: Vaccination campaigns paid for by an employer are estimated to be cost saving when infection results in at least 1.7 days of absenteeism for each case. A higher mortality rate (due to a more virulent strain, and/or inclusion of at risk adults) would introduce replacement costs, thereby raising the cost saving to the employer if they undertook a vaccination program.