Lecture 1

Question 1

Antigenic drift

Answer 1

Antigenic drift involves point mutations in the hemagglutinin and or neuraminidase genes, encoding envelope glycoproteins, thus reducing the binding affinity of antibodies raised against previous strains. This explains why individuals can be reinfected with influenza and why the content of the seasonal vaccine must be altered annually.
(The accumulation of mutations within the genes that code for antibody-binding sites.)
This results in a new strain of virus particles which cannot be inhibited as effectively by the antibodies that were originally targeted against previous strains, making it easier for the virus to spread throughout a partially immune population.
Antigenic drift occurs in both influenza A and influenza B viruses.

Question 2

Antigenic shift

Answer 2

Antigenic shift is the genetic reassortment of genome segments between animal and human strains leading to the expression of novel hemagglutinin subtypes. It essentially creates a “new” virus to which no pre-existing immunity exists and is the process behind dangerous pan- demics such as the 1918 “Spanish Flu.”
(The process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.)
The term is often applied specifically to influenza, as that is the best-known example, but the process is also known to occur with other viruses, such as visna virus in sheep.[1] Antigenic shift is a specific case of reassortment or viral shift that confers a phenotypic change.

Genetic reassortment of genome segments between human and animal strains.