The "modest" success of an HIV "vaccine (疫苗) clinical trial in Thailand is turning out to be even more modest than originally ad

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问题     The "modest" success of an HIV "vaccine (疫苗) clinical trial in Thailand is turning out to be even more modest than originally advertised.
    Full details of the study, released in Paris, show that the vaccine provides no protection to people at the highest risk of HIV infection. In people at lower risk, the benefits may start to decrease after a year. Furthermore, when the results of the three-year experiment are analyzed using alternative methods,  the protective effect falls short of formal statistical significance.
    Despite the new warning, many AIDS researchers say the findings are still important. Some other observers, however, think the results have been oversold in a potentially damaging way.
    Initial results of the RV144 trial were revealed through a press release and interviews in late September. The presentation in Paris provided much more detail, as does a paper released at the same time by the New England Journal of Medicine, where it will eventually be published.
    The effort to make an HIV vaccine has been dogged(固执的) by failure for two decades. The Thai trial, which employed a two-component vaccine and a total of six injections, was the first to show protection. Only 132 became infected among the 16,402 Thai men and women ages 18 to 30 years old who volunteered for the study.
    The trend suggested that the vaccine provided protection, but the results were not statistically significant by the definition used in most medical research.  When counting only people who received all six injections on schedule, which reduced the total sample by 30 percent, there was also a trend toward protection, although not a significant one.
    When the researchers excluded seven people who were already infected when the trial started, however, the results significantly favored the vaccine. It reduced the chance of becoming infected by 31 percent.
    Nelson L. Michael, an Army physician with the U. S. Military HIV Research Program, said it best reflected a real-world use of the vaccine. Not everyone can be expected to follow a complicated shot schedule perfectly, so it was reasonable to include people who didn’t receive all six injections, he told reporters in Paris. He said it was also reasonable to exclude people who were already HIV-positive before the study began.  
When the researchers excluded seven people who were already infected when the trial started, ______.

选项 A、those seven people were in favor of the vaccine very much.
B、the effect of vaccine was significant.
C、it showed that people were less likely to be infected by taking vaccine.
D、it showed the vaccine can reduce the risk of being infected for all the people.

答案C

解析 根据题干关键词excluded,seven people,infected,started定位到原文倒数第二段:...however, the results significantly favored the vaccine. It reduced the chance of becoming infected by 31 percent.可知接种疫苗的实验者感染的可能性会降低31%,C)项符合原文。
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