Modelling studies have shown that vaccination is an effective measure to reduce infection, hospitalisation, mortality and morbidity. 3 Since the supply of vaccines will be limited at the beginning of the influenza pandemic, prioritisation in the administration of the vaccines has been one of the major components in pandemic preparedness. Governments in different countries have issued consultation documents outlining their proposed vaccination policies. 4 5 In nearly all countries with a preparedness plan, healthcare workers are listed as the priority group for mass vaccination. 6 7 The American College of Physicians position statement supports measures to increase the supply of influenza vaccine and antiviral drugs in the strategic national stockpile. 8 Pre-pandemic H5N1 vaccine is now ready and stockpiled by many countries. The first batch of H1N1 vaccine is expected to be available by the end of 2009 or early 2010. 9 More than 30 governments have placed their orders. 9 For example, Hong Kong has decided to buy five million doses for its population of seven million, and the UK Department of Health has ordered 130 million doses of vaccine for its population of 61 million. However, healthcare workers' acceptance of the H5N1 and H1N1 vaccines is unknown. A survey conducted in May, when the pandemic level was already at phase 5, revealed that the general public in Hong Kong did not perceive swine flu (H1N1 influenza) as a threatening disease and did not think an outbreak to be highly likely. 10 The uptake of pre-pandemic vaccination among healthcare workers is a concern as the uptake of seasonal influenza vaccine is often low. In most studies, fewer than 60% of healthcare workers were vaccinated against seasonal influenza in various clinical settings. The most common barriers were fear of side effects, uncertainty about the vaccine's efficacy, and misconceptions about the vaccination and the infection. [11] [12] [13] [14] [15] One study in the UK of 520 participants found that 57.7% of healthcare workers expressed willingness to accept vaccination with the stockpiled H5N1 vaccine. Willingness was associated with perceived risk and benefits, and previous seasonal vaccination. 16 The aim of our study was to investigate the stated acceptability of pre-pandemic vaccination (H5N1 or H1N1 vaccine) and its associated factors among public hospital based healthcare workers in the departments of accident and emergency medicine, internal medicine, and paediatrics in Hong Kong. We also investigated the effect of escalation of the WHO pandemic influenza alert level on the acceptability of pre-pandemic vaccination.