Legislative Analysis of AB 2109

Link is http://www.leginfo.ca.gov/pub/11-12/bill/asm/ab_2101-2150/ab_2109_cfa_20120501_150815_asm_comm.html

Here is a short exerpt:
)Rationale  . According to the author, this bill preserves a
            parent's option to exempt their child from immunization
            requirements and ensures that a decision to do so is an
            informed one, based on accurate and up-to-date information
            regarding individual and public health risks of not immunizing
            their child.  According to the author, the number of vaccine
            exemptions has increased dramatically in the last decade,
            leading to real concern about the loss of "herd immunity" and
            potential for serious disease outbreaks, particularly in
            school classrooms and communities whose exemption rates can
            exceed 40%. He indicates that misinformation widely available
            on the internet and sensationalist media reports have made it
            more difficult for parents to receive accurate, fact-based
            information about vaccines and to ascertain what information
            is reliable.  In addition, he indicates the bill will preserve
            the right to exemption for those with deeply held beliefs,
            while deterring parents who may request an exemption out of
            convenience.  Under current law, exemption only requires a
            parent's signature and is simpler than submitting proof of
            vaccination.  

            This bill is supported by a wide range of public health
            agencies and medical associations, and is co-sponsored by the
            California Medical Association, California Immunization
            Coalition, American Academy of Pediatrics, and the Health
            Officers Association of California.