«لَا عَدْوَى وَلَا طِيَرَةَ»
There is no contagion operating independently and necessarily, and no effective superstition in evil omens.
«فِرَّ مِنَ الْمَجْذُومِ فِرَارَكَ مِنَ الْأَسَدِ»
Avoid a person affected by leprosy as you would flee a lion.
At first sight, the first statement may seem to negate disease transmission, while the second recommends avoidance. The opposition diminishes when each meaning is properly determined. Taking protective precautions and denying that causes operate with autonomous, unfailing power are not the same claim.