In the clusters of never vaccinated, other vaccination history and vaccinated with intent, there were significant differences in knowledge related to general information, high-risk groups and vaccination of recommended groups with P values of <0 . 001, <0 . 003 and <0 . 006, respectively. On average those never vaccinated had the lowest score while those vaccinated with intent had the highest scores across all knowledge items. For only one item of risk perception, i.e. personal vulnerability to illness, was there a significant difference between the clusters of never vaccinated and other vaccination history and between never vaccinated and vaccinated with intent (P<0 . 000 respectively). Those never vaccinated had the lowest average score. There was no statistically significant difference in the knowledge and risk perception item scores between the two vaccinated clusters. However, the newly vaccinated usually had higher scores than those of the continuously vaccinated except for one item, i.e. the vaccination of recommended groups. Similarly, for the two unvaccinated clusters there was no difference for knowledge scores, but there was a significant difference in one risk perception item, i.e. personal vulnerability to illness (P=0 . 001). Those never vaccinated had a lower score for this item than those who used to be vaccinated and they were also less knowledgeable compared to the other group. Tables  4 and 5 .