Attenuated virus
To attenuate is to weaken or to make (or become) thin.
The word derives from a combination of the Latin prefix 'ad-,' meaning 'to' or 'toward,' and 'tenuis,' meaning 'thin.'</P> The use of 'attenuate' in medicine is not new.
In the 16th century, eating dried figs was claimed to attenuate the body fluids.</P> Now 'attenuate' refers to procedures that weaken an agent of disease (a pathogen).
An attenuated virus is a weakened, less vigorous virus.
A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus, a virus capable of stimulating an immune response and creating immunity but not causing illness.