 animal cells these chicken cells again and again what you're doing is you're essentially you're weakening the effect of the virus on a human it's still a virus and it's still a virus that you can actually then take and put inside of a human the thing is it's just not going to cause the same sort of disease that it would if it were like really virulent and very strong it's essentially weakened this is called attenuation you're kind of like turning down the knob or something the volume on this virus it's like you turn down the knob