The other 2 arteries that bring blood to the brain, called the vertebral arteries, supply the brainstem. Plaque in the vertebral arteries is much less likely to break off and cause a stroke, but narrowing in the vertebral arteries can cause problems if the brainstem does not get enough blood flow.
A child should receive the first shot when he is between 12-15 months, and the second when he's between 4-6 years of age. If you're not sure if you have had the diseases or the vaccines (prior to 1971 it was given in three separate shots), you can get the MMR vaccine as an adult.
In countries where transmission of hepatitis B from mother to child is common, these infants should be immunized against the disease at birth. The remaining doses of polio vaccine and the combination diphtheria, pertussis, tetanus vaccine (DPT) should be given three times before the age of one: at six weeks, 10 weeks and 14 weeks. Due to inherited immunity, measles vaccines are typically given at nine months.