Objective: To assess the acceptability of pre-pandemic influenza vaccination among healthcare workers in public hospitals in Hong Kong and the effect of escalation in the World Health Organization's alert level for an influenza pandemic.

Design: Repeated cross sectional studies using self administered, anonymous questionnaires

Setting: Surveys at 31 hospital departments of internal medicine, paediatrics, and emergency medicine under the Hong Kong Hospital Authority from January to March 2009 and in May 2009

Participants: 2255 healthcare workers completed the questionnaires in the two studies. They were doctors, nurses, or allied health professionals working in the public hospital system.

Main outcome measures: Stated willingness to accept pre-pandemic influenza vaccination (influenza A subtypes H5N1 or H1N1) and its associating factors.

Results: The overall willingness to accept pre-pandemic H5N1 vaccine was only 28.4% in the first survey, conducted at WHO influenza pandemic alert phase 3. No significant changes in the level of willingness to accept pre-pandemic H5N1 vaccine were observed despite the escalation to alert phase 5. The willingness to accept pre-pandemic H1N1 vaccine was 47.9% among healthcare workers when the WHO alert level was at phase 5. The most common reasons for an intention to accept were "wish to be protected" and "following health authority's advice." The major barriers identified were fear of side effects and doubts about efficacy. More than half of the respondents thought nurses should be the first priority group to receive the vaccines. The strongest positive associating factors were history of seasonal influenza vaccination and perceived risk of contracting the infection.

Conclusions: The willingness to accept pre-pandemic influenza vaccination was low, and no significant effect was observed with the change in WHO alert level. Further studies are required to elucidate the root cause of the low intention to accept pre-pandemic vaccination.