Final answer:
To find the percentage of children not vaccinated, subtract the percentage of children vaccinated from 100%.
Step-by-step explanation:
To find the percentage of children not vaccinated, we need to subtract the percentage of children vaccinated from 100%. According to the public health officials, 90.5% of children have been vaccinated against measles. This means that 100% - 90.5% = 9.5% of children were not vaccinated. Therefore, the percentage of children not vaccinated is 9.5%.