Grayson's test was negative. He does not want to accidentally bring the virus to his grandparents, so he plans to retest if there is a 1% or greater chance that he has the virus. Should he take another test?

Yes, Grayson should take another test since he does not want to risk potentially exposing his grandparents to the virus. If there is even a small chance that he is carrying the virus, it is better to err on the side of caution and take another test to ensure that he is not inadvertently spreading the virus to others.