Background: Objectives of this study were 1. To review the impact of the Institutional Chickenpox Prevention Program (ICPP) at National University Hospital (NUH), Singapore from Jan 2010 – Jun 2014; 2. To compare the costs of different chickenpox vaccination strategies using a deterministic model; in a 1000 bedded tertiary care university hospital with total staff strength of approximately 7300 in Singapore, a country with a diverse population and a high incidence of adult chickenpox. Methods: Retrospective audit of incidence, contact tracing data, deterministic modelling to predict number and cost of future varicella infections. Results: There were a total of 51 cases of chickenpox, 15 among staff and 36 among inpatients from Jan 2010 to Jun 2014, (average 3.3 staff per year) with two secondary nosocomial transmissions. The median number of staff contacts per patient index case was 4 (IQR 213). Total direct cost incurred for diagnosing and treating the Chickenpox cases was 70,001.7 USD (IQR 248.51961.8 per index); while the total personhours lost were 7,573 (IQR 28229 per index). Cost of chickenpox infection in high risk wards was four times higher with twice as many manhours lost as compared with general wards. Maximizing staff immunity to VZV helped minimize outbreaks in deterministic model. Conclusions: Nosocomial Chickenpox continues to add significant burden to NUH in terms of costs and man hours lost. Deterministic model shows that maximizing staff immunity to VZV would minimize outbreaks. Locally, additional strategies targeting healthcare worker cohorts in high risk areas and from countries with low VZV seroprevalence, may be most cost effective.

Keywords: Varicella; Chickenpox; Singapore; Hospital Vaccination Policy; Vaccination of Healthcare Workers; Health Policy; Infectious Diseases; Hospital Infection Control.