Antigenic shift

The adamantane moiety is of medicinal chemical interest because of its inertness, compactness relative to lipid solubilizing character, and symmetry. Considerable interest, therefore, was engendered by the finding that amantadine (78) was active for the chemoprophylaxis of influenza A in man. There are not many useful chemotherapeutic agents available for the treatment of communicable viral infections, so this finding led to considerable molecular manipulation. The recent abrupt end of the National Influenza Immunization program of 1976 prompted a new look at the nonvaccine means for prophylaxis or treatment of respiratory tract infections due to influenza A, especially in that the well-known antigenic shift or drift of the virus obviates usefulness of the vaccine but not amantadine. 

However, infrequently a mutation arises by genetic reassortment of viruses from different animal hosts ( Antigenic Shift ) whereby an entirely new gene for one of the surface glycoproteins is generated that is significantly different (-50%) in amino acid sequence from the parent virus. This is the mechanism by which new subtypes of influenza arise and are primarily responsible for the major pandemics that occur. 

It has been reported that the antigenic shifts are manifested in hemagglutinin and neuraminidase, two glycoproteins found on the surface of the influenza virion. It is suggested that the hemagglutinin binds the virus to t he target cell and when the hemagglutinin function is inhibited... 

Current recommendations for the use of influenza vaccine in adults are based on a single injection. This may not be valid in case of a new pandemic caused by an antigenic shift of the influenza virus. Currently, the only group for whom a second dose is recommended comprises children who have never been immunized. However, when two-dose regimens in adults have been studied, the second dose of vaccine has not been associated with higher rates of reactions than the first. People who have a stronger local reaction after a first injection are more likely to have another such reaction after a second injection (31). 

Because antigenic shifts (on - ojf,ojf- on) seem to be enhanced by multiple passaging of cells, it seems... 

Antigenic shift Process of antigenic variation probably caused by a reassortment of viral genes. 

Antigenic variation Mutations of influenza viruses that occur by antigenic drift and antigenic shift. 

---