Yes, a fraction with a numerator that is prime can still be simplified. The definition of a prime number is that it's only two factors are 1 and itself. If the numerator is prime, it can still be reduced or simplified because it can be divided by itself to get 1.
For example, the number 7 is a prime number. It's only two factors are 7 and 1. The fraction 7/14 is a fraction where numerator is prime.
