"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.
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)
Disadvantages
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"
References
Badgett, MR. Oct 2002 Journal of Virology "Evolutionary dynamics of viral attenuation" [1]
Global Polio Eradication Initiative: Advantages and Disadvantages of Vaccine Types [2]
