问答题

Passage 4　　Is this the last gasp for the tobacco industry? Scientists have come up with a vaccine that can block the effects of nicotine for up to a year. The vaccine will initially be targeted at the 85% of smokers who want to give up the habit.Although the drug would not take away the nicotine craving, cigarettes would become completely unsatisfying, making it pointless to smoke them.　　The drug could also be used to vaccinate youngsters before they even started smoking. Most adults who smoke began the habit while in their teens, so an annual vaccination for those aged 12 to 20 could prevent the industry recruiting new customers. “The potential for this kind of drug is huge,” said John Shields, senior vice-president of research at Cantab, the British developers.　　Making such a drug available to the public would be a landmark in the history of vaccines. Until now almost all vaccines have been targeted at micro-organisms such as viruses and bacteria. It would be the first time this sort of approach had been used to alter behaviour on such a potentially large scale. Vaccination depends on activating the immune system to recognize and destroy an invading organism or molecule. Previous attempts to develop a vaccine against nicotine have foundered because the nicotine molecule was too small to be recognized. The solution adopted by Cantab—and by Nabi, a rival American firm conducting similar research—is to attach the nicotine molecule to a much larger one.　　Cantab’s vaccine uses a protein stripped from the toxin produced by cholera bacteria. The protein is known to be safe because it is the basis for the cholera vaccine. Between one and four nicotine molecules are attached to each protein molecule, making them large enough for the body’s defences to recognise them as a hostile invader. Once alerted, the immune system starts to make antibodies specifically targeted for nicotine. They then bind to every nicotine molecule they can find and destroy them. It means that hardly any nicotine can pass from the blood into the brain where it would normally have its effect. Cantab has already started tests using a trial version of the vaccine and plans full-scale trials early next year. A similar vaccine, aimed at helping cocaine addicts, is already well into its final trials.　　Frank Stonebanks, a spokesman for Nabi which is about to commence similar trials, said he foresaw a day when parents would get their children vaccinated against smoking in the way that most are inoculated today against tuberculosis. “Such drugs would also have huge potential in the Third World where tobacco addiction costs people a much bigger proportion of their income,” he said.　　Both companies emphasise that it will be at least three years before a vaccine becomes widely available. It would probably be used in conjunction with behavioural therapy since many smokers light up for social reasons as well as addictive ones. The development coincides with a sharp increase in smoking among youngsters. In the past three decades the number of smokers has been falling steadily but the mid-1990s saw a gradual increase in the number of child smokers, especially teenage girls. Government figures show that every day about 450 British youngsters start smoking while another 330 adults die from tobacco-related illnesses such as lung cancer and heart disease. Half of all smokers in Britain die prematurely because of their habit.　　1. What can we learn about the basic principle of vaccination from the passage?　　2. What is nicotine vaccine? What is the major difference between nicotine vaccine and other medical vaccines?　　3. What was the major difficulty in developing nicotine vaccine? How was it overcome?