The outbreak of swine flu that was first detected in Mexico was declared a global epidemic on June 11, 2009. It is the first worldwide epidemic (1) _____ by the World Health Organization in 41 years.

    The heightened alert (2) _____ an emergency meeting with flu experts in Geneva that assembled after a sharp rise in cases in Australia, and rising (3) _____ in Britain, Japan, Chile and elsewhere.

    But the epidemic is “ (4) _____ ” in severity, according to Margaret Chan, the organization’s director general, (5) _____ the overwhelming majority of patients experiencing only mild symptoms and a full recovery, often in the (6) _____ of any medical treatment.

    The outbreak came to global (7) _____ in late April 2009, when Mexican authorities noted an unusually large number of hospitalizations and deaths (8) _____ healthy adults. As much of Mexico City shut down at the height of a panic, cases began to (9) _____ in New York City, the southwestern United States and around the world.

    In the United States, new cases seemed to fade (10) _____ warmer weather arrived. But in late September 2009, officials reported there was (11) _____ flu activity in almost every state and that virtually all the (12) _____ tested are the new swine flu, also known as (A) H1N1, not seasonal flu. In the U. S., it has (13) _____ more than one million people, and caused more than 600 deaths and more than 6,000 hospitalizations.

    Federal health officials (14) _____ Tamiflu for children from the national stockpile and began (15 ) _____orders from the states for the new swine flu vaccine. The new vaccine, which is different from the annual flu vaccine, is (16) _____ ahead of expectations. More than three million doses were to be made available in early October 2009, though most of those (17) _____ doses were of the FluMist nasal spray type, which is not (18) _____ for pregnant women, people over 50 or those with breathing difficulties, heart disease or several other (19) _____. But it was still possible to vaccinate people in other high-risk groups: health care workers, people (20) _____ infants and healthy young people.

答案精析：形容词辨析题。空格前的those代指前半句中的More than three million doses，也就是前文提到的The new vaccine（新疫苗）。前文说到新疫苗比预期提前上市，空格前半句还指出，这种新疫苗在2009年10月初将有超过三百万种剂量可供使用，也就是说这次使用应该是首次使用，in early October 2009表示新疫苗首次使用的时间。故本空应填入initial，和前文首次使用形成对应关系。

错项排除：由上述分析可知，这种疫苗是新的，A项prevalent 和B项principal都不能表示出疫苗是新的这一特点，不符合文意，故排除。该疫苗只是针对流感病毒新制成的，文章并没有针对疫苗的制作是否是创新的进行说明，故C项错误。