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
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
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
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.
（来源:VOA 英语点津 Annabel 编辑）