What are difference between antigen drift and antigenic shift?

Antigen drift and antigenic shift refer to changes in the influenza virus that affect its ability to be recognized by the immune system. Here's the difference between the two:

Antigen drift:

- Gradual and continuous process: Antigen drift occurs gradually and continuously over time. Small mutations accumulate in the viral genome, specifically in the genes that code for the surface proteins hemagglutinin (HA) and neuraminidase (NA).

- Minor changes: The changes in the viral proteins during antigen drift are relatively minor. These mutations can lead to slight alterations in the structure of the HA and NA proteins, but the overall structure remains similar.

- Immune evasion: The gradual changes in the viral proteins may allow the virus to evade pre-existing immunity. This means that individuals who have previously been exposed to the influenza virus or vaccinated against it may have decreased protection against the newly drifted strains.

Antigenic shift:

- Abrupt and significant change: Antigenic shift occurs when there is a sudden and significant change in the viral proteins, particularly the HA or NA proteins. This happens when segments of the viral genome encoding these proteins are replaced by corresponding segments from a different influenza virus strain.

- Major changes: The changes in the viral proteins during antigenic shift are significant, leading to a new or dramatically altered version of the HA and NA proteins. This can result in the emergence of a new strain of influenza that is very different from previous strains.

- Pandemic potential: Antigenic shift can lead to pandemics, as the new strain may be able to infect a large proportion of the population, even those who have immunity to previous strains. The shift in viral proteins can result in a lack of cross-protection, making the existing vaccines and immunity ineffective against the new pandemic strain.

In summary, antigen drift involves minor gradual changes in the viral proteins, leading to a gradual decrease in the effectiveness of immunity over time. Antigenic shift, on the other hand, involves sudden and significant changes in the viral proteins, potentially resulting in the emergence of new pandemic strains capable of infecting a large population.