attenuated

Attenuated is the past participle of attenuate and functions as an adjective meaning weakened or reduced in force, effect, or value. The term appears across disciplines to describe conditions or objects that have been made less harmful, intense, or prominent than their original form.

In biology and medicine, an attenuated pathogen is one that has been weakened so that it no longer causes disease in healthy individuals, or causes only a milder illness. Attenuation is often achieved by growing a virus or bacterium under conditions that reduce its virulence, through passage in nonhuman hosts or cell cultures, or by targeted genetic modification. Live attenuated vaccines use such organisms to provoke a strong immune response while minimizing disease risk. Examples include vaccines for measles, mumps, rubella, varicella, and certain oral polio formulations. Although generally safe, attenuated vaccines carry a small risk of reversion to virulence and are typically avoided in severely immunocompromised individuals.

In physics, engineering, and acoustics, attenuation denotes the loss of signal strength, intensity, or sound pressure as a wave propagates through a medium. It is described by the attenuation coefficient and is often expressed in decibels per unit length. Factors such as absorption, scattering, and geometric spreading contribute to attenuation. Attenuation is central to transmission line design, telecommunications, medical imaging, and seismology, where understanding how and why signals weaken is essential for interpretation and system performance.