OPT- it would be exempted : SS and Medicare, it depends how is your HR coordinate to you. Some of the HR manager is not allowed to deduct those tax. You have suppose to get back once you filed annual tax return with reasonable supporting documents to IRS. Then, you will get back your deposited tax against SS and Medicare, after couple of months.

However, H1B- has  suppose to every taxes (including SS 6.20 % and medicare 1.45% in additional other normal tax (Fed, State, SUI, DBL, etc and any othe local taxes)

Thanks.