…is 2.5 months of high intensity training going to reinfect me?
Yes it would, but there’s good news. You shouldn’t train for a half-marathon that way anyway.
If your goal event is longer than 90 seconds, then the training methods are largely the same. (Ask Michael Phelps… His coach has a philosophy similar to ours here at UA.)
For a 90-minute event, you should limit high-intensity training to 5-7% of your total training time. So in a 10-hour training week, high-intensity should be no more than 30-45 minutes in order to maintain your aerobic capacity (base).
For example, when Moses Mosop ran 2h03m in his first marathon, only 5% of his training was high-intensity (above aerobic threshold).