the act of attenuating or the state of being attenuated.

the process by which a virus, bacterium, etc., changes under laboratory conditions to become harmless or less virulent.

Physics . a decrease in a property, as energy, per unit area of a wave or a beam of particles, occurring as the distance from the source increases as a result of absorption, scattering, spreading in three dimensions, etc.

noun

depletion , devitalization , enervation , enfeeblement , impoverishment