For parents living in North America and other developed countries, the choice not to have children immunized is a luxury and a privilege. As this map makes painfully clear, there are many parts of the world where it's the inaccessibility of vaccines that's the problem.
This map was produced by Benjamin Hennig and Save the Children using information found in Finding the Final Fifth: Inequalities in Immunization (2012).
It looks strikingly similar to a map showing child mortality under age 5:
[ via Vox ]