I mostly agree with Audax and entreat about heavy metals being all around us. The difference with vaccines is that they go directly into the body, bypassing the first lines of defence provided by our skin and stomach.

It's a matter of weighing up the risks & benefits and deciding what you are comfortable with for your child. A book I found useful is "The Vaccine Book" by Dr Robert Sears. He tells you about both the disease and the vaccine and lists the ingredients of each vaccine. I've been using it to determine our own vaccine schedule.