In 1958, a new strain of influenza A with different HA and NA was identified and antigenic shift was discovered; the need for a trivalent vaccine was recognized. Technical advances have made it ...

These strains occur because of the phenomenon known as antigenic shift, in which humans are infected with avian influenza viruses or viruses that contain a combination of genes from human and ...

When two or more existing strains combine to form a new strain that is called antigenic shift. Such a significant mutation occurs, for instance, when a flu virus from a bird and a flu virus from ...

In 1958, a new strain of influenza A with different HA and NA was identified and antigenic shift was discovered; the need for a trivalent vaccine was recognized. Technical advances have made it ...