Attenuated virus

"Attenuated" redirects here. For the bacterial use of the term, see Attenuator (genetics)

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The verb "attenuate" means "to become weak."

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 :

• Tissue culture
• Embryonated eggs
• live animals

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)

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

References

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