In Washington, an exemption does not mean unvaccinated. Only 4.1% of Washington students have a non-medical exemption on file*. An exemption is required even if only one injection in a series is missing. Washington requires 16 injections; a student with 15 of 16 injections, and a student with 0 of 16 injections both file an exemption. Very few children have exemptions for all vaccines. The rate of exemption for individual vaccines varies from 2.6-3.2%. So any individual vaccine has at least 96.8% compliance.
*All statistics are from the Washington Department of Health. http://www.doh.wa.gov/DataandStatisticalReports/Immunization/SchoolReports