Oregonians for Healthy Children says the numbers from this year's statewide exclusion day show a 6.4% rate of kindergartners exempted from required immunizations on religious grounds.   Spokeswoman Anne Stone says 17 of those counties passed the 6% threshold, which lowers "herd immunity" for some vaccine-preventable diseases.  The organization is pushing a policy change. Senate Bill 132 would require parents to certify that they have completed vaccine education, through the state or their physician,  before their children could get the exemption.