Why this state is lagging behind the rest of the US in routine childhood vaccinations

"For all four major vaccines -- measles, mumps and rubella (MMR); diphtheria, tetanus and acellular pertussis (DTaP); poliovirus (polio) and varicella (chickenpox) -- Idaho had the lowest percentage of kindergartners who met school requirements for vaccinations, all around 81% compared to a nationwide rate of 93%."