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**Change of species specificity
 
**Change of species specificity
 
*'''Drift''' is the evolution of a virus within its subtype, evidenced by the changing strains of human flu from year to year
 
*'''Drift''' is the evolution of a virus within its subtype, evidenced by the changing strains of human flu from year to year
**Each H spike carries 4 antigenic region, and a change in any region results in drift
+
**Each H spike carries 4 antigenic regions, and a change in any region results in drift
 
**Viral RNA is constantly evolving to evade immune detection and destruction
 
**Viral RNA is constantly evolving to evade immune detection and destruction
 
*Vaccination schemes are affected by both shift and drift:
 
*Vaccination schemes are affected by both shift and drift:
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