Positive and negative attitudes-39% (n=117) of participants believed that vaccination would be effective at preventing influenza A/H1N1, 63% (n=189) erroneously believed that efficacy of influenza A/H1N1 vaccine had been confirmed by clinical trials, and 16% (n=49) believed that it is necessary for everyone in Hong Kong to take up vaccination against influenza A/H1N1 (49%, n=146, not quite necessary and 32%, n=95, completely unnecessary; table 2).