All I know is my daughter opted out, one time in 2003 and never has to opt out again of ANY immunizations. It was the law at the time. Now if you didn’t opt out in 2003, you can’t do that, it’s every year since the nice RINOs and democrats changed it in 2007..
The good news is that they didn’t change the 2 year requirement in 2007, according to the DSHS website
http://www.dshs.state.tx.us/immunize/docs/faq_exemption.pdf