Changes

**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: