Yes, if the tissue has been adequately penetrated by the formalin. So it depends on the size and thickness of the tissue, and the amount of formalin present. The fixing of tissue by formalin is a chemical reaction and it can be exhausted if not enough formalin is present. Basically the center of the tissue may not have been reached. However, 48 hours is plenty of time for the average specimen. HCV, HBV, and HIV should have been killed by now.