免疫(immunity)

是机体的生理性保护机制，其本质为识别自身，排除异己；具体功能包括防御感染，清除衰老、损伤或死亡的细胞，识别和清除突变细胞。

Transpantation immunity

Immunity

Innate immunity

Adaptive immunity

Although we already know a great deal about influenza, and although the World Health Organization is constantly collecting detailed information from its chain of influenza reference laboratories throughout the world, it is extremely difficult for epidemiologists (流行病专家), who study infectious disease, to predict when and where the next flu epidemic will occur, and how severe it will be.
There are three kinds of influenza virus, known as A, B and C. Influenza C virus is relatively stable and causes mild infections that do not spread far through the population. The A and B types are unstable, and are responsible for the epidemics that cause frequent concern. Following any virus attack, the human body builds up antibodies which confer immunity to that strain of virus, but a virus with the capacity to change its character is able to by-pass this protection. Variability is less developed in the influenza B virus, which affects only human beings. An influenza B virus may cause a widespread epidemic but will have little effect if introduced into the same community soon afterwards, since nearly everyone will have built up antibodies and will be immune. The influenza A virus, which affects animals also, is extremely unstable and is responsible for some of the worst outbreaks of the disease, such as the unparalleled pandemic, or world epidemic, of 1918-1919, when about half the world’s population were infected and about twenty million people died, some from pneumonia caused by the virus itself and some from secondary complications(并发症) caused by bacteria.
Accurate prediction is difficult because of the complication of the factors. A particular virus may be related to one to which some of the population have partial involved immunity. The extent to which it will spread will depend on factors such as its own strength, or virulence, the ease with which it can be transmitted and the strength of the opposition it encounters. Scientists, however, have a reliable general picture of the world situation. Influenza A attacks us in waves every two or three years, while influenza B, which travels more slowly, launches its main assaults every three to six years. The outbreaks vary from isolated cases to epidemics involving a tenth or more of the population. We may confidently prophesy that sooner or later large numbers of people will be feeling the unpleasant effects of some kind of influenza virus.

Which of the following is NOT mentioned as a factor contributing to the extent to which a virus spreads（）

A:the strength of the virus B:the strength of the opposition the virus encounters C:the ease with which the virus can be transmitted D:the immunity the virus can induce

nonspecific immunity和specific immunity

The government has ordered 195 million doses of vaccine, 45 million of which will be delivered by mid - October. But because most people lack prior immunity to the new H1N1 virus, officials expect that two injections will probably be necessary, spaced three weeks apart. Clinical trials are currently underway to confirm whether two shots are actually needed and to determine the optimal dose. Resuhs from those trials will be available in late September or early October. But even after receiving the vaccine, a person will take at least five weeks to develop full immunity.
Two injections of the vaccine will probably necessary because.

A:there are more than enough doses of vaccine for all Americans. B:people will develop full immunity right after two injections. C:a single injection will not enable people to develop immunity. D:most people lack prior immunity to the new H1 N1 virus.

Although we already know a great deal about influenza, and although the World Health Organization is constantly collecting detailed information from its chain of influenza reference laboratories throughout the world, it is extremely difficult for epidemiologists (流行病专家), who study infectious disease, to predict when and where the next flu epidemic will occur, and how severe it will be.
There are three kinds of influenza virus, known as A, B and C. Influenza C virus is relatively stable and causes mild infections that do not spread far through the population. The A and B types are unstable, and are responsible for the epidemics that cause frequent concern. Following any virus attack, the human body builds up antibodies which confer immunity to that strain of virus, but a virus with the capacity to change its character is able to by-pass this protection. Variability is less developed in the influenza B virus, which affects only human beings. An influenza B virus may cause a widespread epidemic but will have little effect if introduced into the same community soon afterwards, since nearly everyone will have built up antibodies and will be immune. The influenza A virus, which affects animals also, is extremely unstable and is responsible for some of the worst outbreaks of the disease, such as the unparalleled pandemic, or world epidemic, of 1918-1919, when about half the world’s population were infected and about twenty million people died, some from pneumonia caused by the virus itself and some from secondary complications(并发症) caused by bacteria.
Accurate prediction is difficult because of the complication of the factors. A particular virus may be related to one to which some of the population have partial involved immunity. The extent to which it will spread will depend on factors such as its own strength, or virulence, the ease with which it can be transmitted and the strength of the opposition it encounters. Scientists, however, have a reliable general picture of the world situation. Influenza A attacks us in waves every two or three years, while influenza B, which travels more slowly, launches its main assaults every three to six years. The outbreaks vary from isolated cases to epidemics involving a tenth or more of the population. We may confidently prophesy that sooner or later large numbers of people will be feeling the unpleasant effects of some kind of influenza virus.

Which of the following is NOT mentioned as a factor contributing to the extent to which a virus spreads（）

A:the strength of the virus B:the strength of the opposition the virus encounters C:the ease with which the virus can be transmitted D:the immunity the virus can induce