For 5-years you are exempt from residency. You do not pay Social Security and Medicare taxes. You do pay income taxes. You must file non-resident tax return and will not get standard deduction, and there is no special deduction as per tax treaty:
"A student, apprentice, or business trainee who is a resident of Ireland immediately before visiting the United States and is in the United States for the purpose of full-time education at a recognized educational institution or full-time training is exempt from U.S. income tax on amounts received from sources outside the United States for the individual's maintenance, education, or training.
Apprentices and business trainees are entitled to the benefit of this exemption for a maximum period of 1 year."
Read:
Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents