Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Antigenic drift and shift.
| Drift | Shift |
|---|---|
| Minor change within subtype | Major change, new subtype |
| Point mutations | Exchange of gene segments |
| Occurs in A and B subtypes | Occurs in A subtypes only |
| May cause epidemics | May cause pandemic |
| Example: A/Fujian (H3N2) replaced A/Panama (H3N2) in 2003-2004 | Example: H3N2 replaced H2N2 in 1968 |
