AskDefine | Define attenuated

Dictionary Definition

attenuated adj
1 of an electrical signal; reduced in amplitude with little or no distortion
2 reduced in strength; "the faded tones of an old recording" [syn: attenuate, faded, weakened]

User Contributed Dictionary



  1. past of attenuate


  1. Made, or become weak; subject to attenuation
  2. Long and tapering (especially of leaves)

Extensive Definition

"Attenuated" redirects here. For the bacterial use of the term, see Attenuator (genetics)
Attenuation in virology is reducing the virulence of a virus, whilst keeping it viable (or 'live'), for the purpose of creating a vaccine. It is the counterpart of the vaccines produced by 'killing' the virus (inactivated vaccine)
Viruses may be attenuated via passage of the virus through a foreign host, such as :
The initial viral population is applied to the foreign host. In all likelihood one of these will possess a mutation that enables it to infect the new host. However this mutant will normally have a lower virulence in the original host, as the rest of the genetic information for interacting with the host hasn't changed, enabling it to infect them, but cause less damage, and so it acts as a vaccine.

Advantages of Attenuated Vaccines

  • Activates all phases of the immune system (for instance IgA local antibodies are produced)
  • Provides more durable immunity; boosters are not required
  • Low cost
  • Quick immunity
  • Easy to transport/administer (for instance OPV for Polio can be taken orally, rather than requiring a sterile injection by a trained healthworker, as the inactivated form IPV does)


  • Major Disadvantage -Secondary mutation can cause a reversion to virulence
  • May still be able to cause disease in immunocompromised patients (e.g. those with AIDS)
  • Sometimes may not work in tropical areas
  • Can be difficult to transport due to requirement to maintain conditions (i.e. temperature) at which the virus can "survive"


attenuated in Chinese: 減毒性病毒

Synonyms, Antonyms and Related Words

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