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  • Have you ever wondered why you need a flu vaccination each year? Unlike other

  • viruses that are relatively stable, influenza viruses are always changing.

  • Influenza genes drift to create new viruses.

  • This means that the infection-fighting antibodies that your body makes in

  • response to the flu vaccine may only protect you for one flu season.

  • After that, circulating flu strains may change and make the old vaccine

  • ineffective. A new vaccine is needed to match the new viruses.

  • The heart of a flu virus has eight spring-like segments called RNA.

  • These are the genes that encode parts of the virus.

  • Around the RNA are different proteins.

  • The proteins involved in drift are called Hemagglutinin and Neuraminidase.

  • Scientists call them HA and NA.

  • There are 16 subtypes of HA proteins and nine of NA.

  • From these protein combinations, scientists name influenza A viruses. For example,

  • an H5N1 virus contains hemagglutinin subtype 5 and

  • neuraminidase subtype 1.

  • If a person has been vaccinated or has a natural immunity against the virus,

  • antibodies will attach to the HA protein,

  • blocking it from infecting human cells and stopping the virus from spreading.

  • Without natural immunity or immunity provided by the correct vaccine,

  • the HA proteins on the virus interact with sugars on the outside of those cells.

  • This creates a bond that allows the virus to enter targeted cells where it can

  • cause infection.

  • When the influenza viruses replicate, they can mutate slightly.

  • Scientists have shown that this leaves small changes in the HA and NA

  • proteins.

  • Over time, as the virus spreads from person to person,

  • these changes accumulate, and the virus drifts from its original form.

  • Eventually, the immune system no longer recognizes the HA proteins from the

  • virus, and the flu vaccine becomes ineffective.

  • Each year, flu vaccine is made to protect against the most common flu viruses

  • predicted to circulate among the population.

  • Historically, scientists have done a remarkable job of matching the vaccine to

  • the circulating viruses.

  • Although there is an effective vaccine,

  • not enough people choose to get it.

  • As a result, influenza sickens between 5 and 20 percent of the U.S.

  • population each year.

  • More than 200,000 people may be hospitalized,

  • and up to 49,000 people may die.

  • That is why health officials recommend flu vaccination before every flu season.

Have you ever wondered why you need a flu vaccination each year? Unlike other

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B2 中高級

流感。獲取(抗原)漂移 (Influenza: Get the (Antigenic) Drift)

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    Ming-Yuan Peng 發佈於 2021 年 01 月 14 日
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