I would feel more comfortable with this if it was an opt-in program. I don't know about all children but I imagine several would prevent their parents from even seeing the letter. So being allowed to "opt out" is null if you never knew it existed to start with.
Similarly I think you would have to be an "absent" parent to not know about the school's policy. Either that or the school has poor practices. Our local health department gives out the flu mist to all students whose parents "opt-in". They send home a written letter, call to inform you of the letter, and send multiple emails about the letter and an online form you can use to give consent. Sometimes it annoys me how thorough our school is but then I hear about stories like this and I'm glad they are.
I don't want anyone giving my children medication with out my consent. I don't feel like I should have to opt-out to revoke my consent. I want to be able to actively give consent and don't ever want my consent to be assumed.
This may sound a little prudish when considering how unlikely it is that a sexually active teenager will want to seek consent. Or how many unwanted pregnancies can be avoided because a child is afraid to get consent. But I feel as though it's my right as a parent to make the decision as to who gives my children medication.
That being said. Both my daughters will be raised in home where they won't have to fear bringing home these types of letters. How they choose to respond to my open mindedness is yet to be determined. But the door will be open.