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→Antigenic Shift and Drift
**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: