"Relief can be claimed for health expenses paid in each tax year, or for the year in which the expenses were incurred. Claims can be in respect of subscription year or tax year but must be consistent every year. Relief is given by way of repayment at the end of the year.
In cases of hardship relief may be granted during the tax year. All such cases will, of course, be subject to lodgement of form Med1 in the normal way, and to review after the end of the year in question."
In other words....yes, you generally have to wait 'til after the end tax year. This is due to Medical Expsnes geing relieveable at your marginal rate of tax and that won't not be known with certainty 'til after the end of the year.