"Since a vaccination is a MEDICAL procedure, Governor Perry is practicing medicine without a license."
The authority is in the Education Code. Same authority that requires all the other vaccinations (measles, mumps, rubella, tetanus) for school kids.
Which was implemented by the Texas legislature, NOT an Executive Order.
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BTW- Where in the Education code does the Governor or the legislature get a medical authority?
(Remember, in order to be a legitimate authority, the People have to give the power to the government, the government doesn't just get to say "We CAN do this")