三级aa视频在线观看-三级国产-三级国产精品一区二区-三级国产三级在线-三级国产在线

您現在的位置: > Language Tips > Audio & Video > Special Speed News  
 





 
Vaccines: How they work
[ 2007-04-20 09:15 ]

This is the VOA Special English Health Report.

Most vaccines are designed with the same goal in mind. That is, to help the body's own defense system prevent a disease by producing antibodies against it. Antibodies are disease-fighting proteins. The immune system produces them in reaction to viruses, bacteria and other invaders.

The vaccine tricks the body into thinking it has already successfully defeated the disease. To activate the immune system, vaccines commonly introduce the disease-causing virus or bacteria into the body. But they use weakened or killed versions.

Weakened viruses are used, for example, in vaccines against chickenpox, measles, mumps and rubella. To prevent polio, the Sabin vaccine uses a weakened form of the virus; the Salk vaccine uses a killed version.

Experts say vaccines that use killed or inactivated virus can be safely given even to people with damaged immune systems.

Researchers may spend years working on a vaccine. They have still not succeeded against, for example, H.I.V., the virus that causes AIDS, or against malaria, but they are trying.

And not all vaccines offer long-term protection. The tetanus vaccine is a good example. It offers protection for only about ten years. Then a person must be immunized again.

Some vaccines are made with animal material. For example, influenza vaccine is grown in chicken eggs. This can be a problem for people who are allergic to eggs. Also, the process is complex.

But things could change in the future. A new study in the Journal of the American Medical Association suggests that flu vaccine could come from insect cells.

Researchers in the United States tested a flu vaccine made from caterpillar cells. The study involved four hundred sixty people. There were two versions of the vaccine, one stronger than the other.

The people were not told whether they were getting the vaccine or a substitute, a placebo. Here is what the scientists reported: Seven people in the placebo group caught the flu. So did two people who received the lower strength vaccine. But no one in the stronger vaccine group got the flu.

Protein Sciences, a vaccine maker, paid for the study. The company plans to begin testing the experimental flu vaccine on a larger group in order to seek government approval.

And that's the VOA Special English Health Report, written by Caty Weaver. For more health news, along with transcripts and audio files of our reports, go to voaspecialenglish.com. I'm Steve Ember.


antibody : 抗體


點擊進入更多VOA慢速

(來源:VOA  英語點津 Annabel 編輯)

 
 
相關文章 Related Stories
 
Choose your degree at an American college Coming to terms with academic titles at US colleges
Studying in the US: Rules about alcohol Once you get into a US college, where to live?
Studying in the US: Four kinds of financial aid
A college handbook just for international students
Life as a teaching assistant in US Coming to America as a Fulbrighter
         
 
 
 
 
 
         

 

 

 
 

48小時內最熱門

     

本頻道最新推薦

     
  Va. Tech gunman video sparks mixed reaction
  The formula for becoming a pharmacist
  Details of Va. Tech gunman's disturbing past emerge
  The Queen《女王》(精講之二)
  爵士小天后:《七年》

論壇熱貼

     
  English etiquette
  請問"萬能膠水"怎么翻?
  "百善孝為先,行孝當及時"用英語怎么說?
  請問‘三九天’英文怎么說
  What do I feel about Canada
  朋友,你在用CHINGLISH寫作嗎??






主站蜘蛛池模板: 欧美精品久久久久久久免费观看 | 欧美激情福利视频在线观看免费 | 国产欧美日韩在线播放 | 一区二区三区精品国产欧美 | 91视频日本 | 尤物视频最新网址 | 亚洲国产成人久久一区二区三区 | 国产伦一区二区三区高清 | 久久欧美精品欧美久久欧美 | 香蕉精品在线 | 日韩精品一区二区三区在线观看 | 麻豆视频免费观看 | 久久久久久久九九九九 | 制服丝袜中文字幕在线观看 | 日韩精品你懂的在线播放 | 欧美色噜噜 | 免费在线看黄网址 | 日韩不卡一级毛片免费 | 亚洲精品一区二 | 最新亚洲精品国自产在线观看 | 女性一级全黄生活片在线播放 | 欧美一区二区三区视频 | 久在草视频 | 国产一线视频在线观看高清 | 日本一级毛片高清免费观看视频 | 色男人的天堂 | 高清一区高清二区视频 | 妞干网这里只有精品 | aaa免费毛片 | 成年免费大片黄在线观看看 | 亚洲国产精品免费视频 | 午夜性刺激片免费观看成人 | 国产精品短篇二区 | 免费观看欧美成人1314色 | 成年美女黄网站色视频大全免费 | 精品日产1区2区 | 一区二区三区网站 | 国产日产欧美一区二区三区 | www国产永久免费视频看看 | 亚洲四区| 成人免费体验区福利云点播 |