avirulent

/eɪˈvɪrjələnt/
adjective
  1. Not harmful or disease-causing; lacking the ability to cause illness (used especially in biology and medicine).
    • The avirulent pathogen did not make the test animals sick.
    • The avirulent strain of the virus was used to create a vaccine.
    • Scientists studied an avirulent form of the bacteria to understand immunity.
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