We found that a lack of knowledge about influenza and vaccination was a strong predictor of nurses' vaccination behaviours, especially for those never vaccinated. This cluster had the lowest knowledge score, suggesting that increasing their knowledge might improve their vaccination behaviours. However, it seems there are 'persistent decliners ' who are in the 'habit ' of not having a vaccination. This suggests that future educational campaigns need to be persistent, durative, and intensive if their vaccination behaviours are to be modified. For those who had been vaccinated in the past but not in the current season, knowledge was also a predictor for their vaccination behaviours, which suggests that current vaccination campaigns have failed to address their misgivings about vaccination to maintain their compliance with the annual vaccination recommendation for HCWs. Between those occasionally vaccinated and continuously vaccinated, knowledge levels were not significantly different but the newly vaccinated in 2009 had on average higher knowledge scores than those continuously vaccinated. This may reflect an increase in their risk perceptions towards influenza due to widespread reporting of the risks in the media encouraging them to be vaccinated for the first time in their lives. This suggests that timing may be crucial to the success of vaccination campaigns making behaviour modification easier. Future studies are required to explore the relationship between the content and timings of vaccination campaigns and nurses' first vaccination uptake.