This results in a new strain that requires yearly reformulation of the seasonal influenza vaccine. Since the late nineteenth century, four occurrences of antigenic shift have led to major influenza pandemics. Antigenic drift: A subtle change in the surface glycoprotein (either hemagglutinin or neuraminidase) caused by a point mutation or deletion in the viral gene. An antigenic shift can lead to a worldwide pandemic if the virus is efficiently transmitted from person to person.Īn example of a “shift” occurred in the spring of 2009, when a novel H1N1 virus with a new combination of genes (from American pigs, Eurasian pigs, birds, and humans) emerged in people and quickly spread, causing a pandemic. Two mechanisms enable viruses to escape the host immune response: antigenic drift and antigenic shift (Weber. The virus tries to avoid or defeat the host defense mechanisms, whereas the host defense tries to eliminate the virus. Shift occurs at varying intervals and likely is the result of reassortment (the exchange of a gene segment) between influenza A viruses, usually those that affect humans and birds.Īntigenic shift results in a new influenza A subtype that is so different from previous subtypes in humans that most people do not have immunity to the new virus. Whereas antigenic drift is the accumulation of small alterations in antigens over a long period of time, antigenic shift is a dramatic and sudden change. Viral infections result in a constant competition between the virus and host to prevail over each other. Source: Griffinstorm, Wikipedia Commons.Īntigenic shift is a major, abrupt change in one or both surface antigens (HA or NA). As a feature emergent from the inability of the hostimmune response to match. Like this lightning storm near New Boston, Texas, antigenic shift involves major, abrupt changes in surface antigens (HA or NA). Antigenic variability is characterized by the emergence of sequence distinct variants within a species, circulating between hosts, within hosts, or temporally across populations, for which adaptive immunity elicited by one strain fails to protect against another.
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