考研究生英语阅读理解精读P—医学.docVIP

2015考研英语阅读理解精读P7—医学 　　Passage 7 　　Shortages of flu vaccine are nothing new in America, but this years is a whopper. Until last week, it appeared that 100 million Americans would have access to flu shots this fall. Then British authorities, concerned about quality-control problems at a production plant in Liverpool, barred all further shipments by the Chiron Corp. Overnight, the U.S. vaccine supply dwindled by nearly half--and federal health officials found themselves making an unusual plea. Instead of beseeching us all to get vaccinated, theyre now urging most healthy people between the ages of 2 and 64 not to. This re-emphasizes the fragility of our vaccine supply, says Dr. Martin Myers of the National Network for Immunization Information, and the lack of redundancy in our system. 　　Why is such a basic health service so easily knocked out? Mainly because private companies have had little incentive to pursue it. To create a single dose of flu vaccine, a manufacturer has to grow live virus in a 2-week-old fertilized chicken egg, then crack the egg, harvest the virus and extract the proteins used to provoke an immune response. Profit margins are narrow, demand is fickle and, because each years flu virus is different, any leftover vaccine goes to waste. As a result, the United States now has only two major suppliers (Chiron and Aventis Pasteur)--and when one of them runs into trouble, there isnt much the other can do about it. A vaccine maker cant just call up and order 40 million more fertilized eggs, says Manon Cox, of Connecticut-based Protein Sciences Corp. Theres a whole industry thats scheduled to produce a certain number of eggs at a certain time. 　　Sleeker technologies are now in the works, and experts are hoping that this years fiasco will speed the pace of innovation. The main challenge is to shift production from eggs into cell cultures--a medium already used to make most other vaccines. Flu vaccines are harder than most to produce this way, but several bio