Concept
Antigenic drift vs shift
Gradual mutation vs abrupt reassortment
an-tih-JEN-ik
High-yield clue
Drift = small gradual point mutations (epidemics); shift = sudden reassortment of gene segments (pandemic potential).
Overview
Two general mechanisms by which surface antigens change to escape existing immunity: antigenic drift is gradual accumulation of point mutations, while antigenic shift is an abrupt exchange of whole gene segments (reassortment). The concept explains why immunity can fail over time.
Classification
- Immunology/virology concept
- Mechanisms of antigenic variation
- Point mutation vs genome reassortment
Lab & identification clues
- Drift underlies the need to update seasonal vaccine strains
- Shift requires a segmented genome so segments can reassort
- Antibody escape follows changes in surface antigens
Associations
- Drift produces yearly epidemic vocabulary
- Shift creates novel antigens the population has not seen
- Reassortment can mix animal and human strains
Commonly confused with
- Antigenic drift vs shift
- Mutation vs reassortment
Your notes
Original microbiology concept summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC/WHO topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment selection, infection-control instructions, or specimen-handling guidance.