This year’s seasonal vaccine contains three influenza viruses — one A (H3N2) virus, one regular seasonal A (H1N1) virus unrelated to the swine flu strain and one B virus.

今年的季节流感疫苗含有三种流感病毒——一种甲型（H3N2）病毒，一种与猪流感毒株无关的常规季节性甲型（H1N1）病毒，以及一种乙型病毒。

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It takes approximately five to six months for the first supplies of approved vaccine to become available once a new strain of influenza virus with pandemic potential is identified and isolated.

一旦鉴定并分离出具有大流行可能的流感病毒新毒株，大约需要5至6个月时间提供首批获批准的疫苗。

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Extensive studies and data analysis of influenza vaccines have only found a well established causal association with the 1976 vaccine that contained an H1N1 swine-influenza-like virus.

经由对流感病毒的进一步研究和数据分析，只发现在1976年含有类似于H1N1病毒的疫苗存在一例具有完整因果联系的案例。

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"There are parts of the flu virus that could be the target of what we would hope eventually could be a universal influenza vaccine."

VOA: standard.2010.07.21

The reason for that is that the influenza virus has a rapid rate of mutation, forcing companies that manufacture the vaccine to make their best guess as to which flu types will be more prevalent in a given season.

FORBES: One Step Closer to a Universal Flu Vaccine?

This year's North American vaccine is made from three viruses: two types of influenza A virus (H3N2 and H1N1) and an influenza B virus.

CNN: Had a flu shot? You'll be OK -- maybe

As of January 5, the CDC said Friday, the predominant virus in the United States was an influenza A (H3N2) virus that matched well with the H3N2 virus represented in the vaccine.

CNN: Had a flu shot? You'll be OK -- maybe