A brief search indicates that only 1-2% of children are unable to receive traditional vaccinations due to allergies or immunocompromised conditions.
I’m willing to bet that the unethical doctors writing exemptions likely have an unbalanced amount of child-vaccination exemptions to administered child-vaccinations ratio. Such discrepancies should be thoroughly investigated.
In other words, if more than 2 out of every 100 children, a particular doctor consults with, are given vaccination exemptions, then something is suspicious.