The World Health Organization (WHO) raised the pandemic alert level on Wednesday evening to phase 5, signaling that the first influenza pandemic in more than 40 years was imminent. That announcement came on a day when the H1N1 swine flu virus continued to spread worldwide, with new cases confirmed in Austria, Germany, Britain, New Zealand and Israel, bringing the global caseload to 148.

The hardest hit countries are still Mexico and the U.S., where the virus is spreading easily from person to person — the main reason behind the WHO's decision to raise the pandemic alert from phase 4 to 5. In the U.S. there are now more than 90 confirmed cases in 10 states, with the first fatality reported on Wednesday morning — a 22-month-old Mexican boy who died in Texas. In Mexico more than 150 people have died of what is suspected to be swine flu, with more than 2,400 suspected infections — though only seven deaths and 26 cases have been confirmed as swine flu in a lab.

But the pandemic threat goes well beyond one or two countries. "An influenza pandemic should be taken seriously because of its capacity to spread rapidly," said WHO director-general Margaret Chan. "We do not have all the answers now. But we will get them."

With the H1N1 swine flu virus seemingly entrenched in both Mexico and the U.S., and continually surfacing elsewhere, a pandemic may be inevitable — flu viruses are extremely transmissible and hard to control. But that hasn't stopped health officials from trying. In the U.S. President Barack Obama said on Wednesday that affected schools "should strongly consider temporarily closing so that we can be as safe as possible," prompting the closure of schools with confirmed cases — involving some 50,000 students — in several states. At his news conference on Wednesday night, Obama also said that "every American should know that their entire government is taking the utmost precautions and preparations."

hose measures include strengthening surveillance of travelers entering the U.S., examining and testing people who might be exhibiting flu-like symptoms and alerting U.S. citizens in Mexico, where the disease still seems to be at its worst. Meanwhile, other countries have placed far stronger restrictions on travel to Mexico, in an effort to cut off the spread of the disease. Cuba and Argentina have temporarily banned flights to and from Mexico, Japan has stopped giving visas to Mexicans who arrive in the country, and France is putting forward a request to suspend all flights between the European Union and Mexico.

In hearings on Wednesday, members of Congress sharply questioned Secretary of Homeland Security Janet Napolitano on the possibility of virtually sealing off the border with Mexico. Said Republican Senator John McCain in a statement, "I continue to believe that all available options to end this crisis must remain under consideration, including closing the border if it would prevent further transmission of this deadly virus."

But Napolitano said the U.S. has no plans to close the border with Mexico, a stance that the Centers for Disease Control and Prevention (CDC) and WHO support and which Obama reiterated at his press conference. "Intensive efforts at the border are not effective means for protecting against an infectious disease," said acting CDC director Richard Besser. Still, if the swine flu continues to worsen in Mexico, it's not hard to see how Obama and other world leaders would come under increasing pressure to try to wall off Mexico — just as an infected patient might be quarantined to prevent the spread of the disease.

Health officials argue that because the H1N1 swine flu virus is already present in so many countries, and readily capable of spreading from person to person, it's far too late to try to isolate one or two countries. Although uninfected countries may be able to delay the introduction of swine flu by imposing draconian limits on international travel, they would not likely be able to stave off the virus for good — and the economic losses resulting from the travel ban may far outweigh any benefits. One 2007 study by the Brookings Institution estimated, for example, that a 95% reduction in U.S. air travel would cost the economy $100 billion a year.

"Once the virus has spread beyond its initial focus, travel restrictions just aren't effective," says Ira Longini, a biostatistician at the University of Washington. With 4,000 flights a day between the U.S. and Mexico, "it's not worth the social disruption it would cause."

That's not to say that very strict restrictions wouldn't have some effect on slowing the virus. In a 2006 study, Harvard epidemiologists John Brownstein and Kenneth Mandl examined the effect of the sharp reduction in air travel after the Sept. 11 attacks on that year's flu season. They found that the initial flight ban and general decline in air travel in the weeks after delayed the onset of the flu season but did little to reduce the overall number of infections and deaths that year.

The data matches computer models run by biostatisticians like Longini, who found that even the strictest limits on air travel would only slow the start of a flu pandemic, not stop its spread. But, again, while that strategy may benefit countries that have not yet been infected with swine flu, there's still no way to know when it would be safe to lift those restrictions. "There's no question that air travel spreads the flu," says Mandl, a physician and researcher at the informatics program at Children's Hospital Boston and an associate professor at Harvard Medical School. "But the impact of limiting flights at this point is difficult compared to the downside of the economic impact."

As far as the U.S.-Mexico border is concerned, attempting to actually close it would be futile, since countless illegal migrants cross over to the U.S. daily. Trying to stop movement may just push travelers, and the spread of the swine flu, underground. It would create a diplomatic headache as well — the Mexican government has already expressed its concern over travel restrictions.

What works better are social-distancing actions on a local level — closing schools, having employees work at home and limiting public gatherings, where the flu can spread easily. Such methods worked during the deadly 1918 Spanish flu — cities that acted quickly to close schools and theaters early in the pandemic had peak death rates 50% lower than cities that acted more slowly. Today doctors could also prophylactically administer antiviral drugs to the close contacts of any swine flu patients, a strategy that has been shown to help prevent the spread of the flu. "Until you start to see really massive clusters, that can be a really effective method," says Longini.

Ultimately, however, in a world as truly interconnected as ours, we can no more cloister a single country than we could cut off a limb. The world has become increasingly one — as the rapid spread of the swine flu virus from country to country shows. "It is really all of humanity that is under threat during a pandemic," says the WHO's Chan. Whatever happens next with the swine flu — whether it burns out or sharpens — we're in this together.

周三晚上,世界衛(wèi)生組織（ WHO ）把流感警戒級(jí)別提高到5級(jí),這就預(yù)示著40多年來(lái)第一次爆發(fā)流感的嚴(yán)重性.當(dāng)天豬流感病毒H1N1繼續(xù)全球蔓延.在奧地利，德國(guó)，英國(guó)，新西蘭和以色列，也發(fā)現(xiàn)并證實(shí)了新的病例,從而使全球的病例達(dá)到148個(gè)。

受災(zāi)最嚴(yán)重的國(guó)家仍然是墨西哥和美國(guó)，在那里病毒很容易人傳人-這是主要原因迫使世衛(wèi)組織作出決定，將流行病警戒級(jí)別由4級(jí)提升到5級(jí).在美國(guó),已經(jīng)有10個(gè)州確診了超過(guò)90個(gè)病例.周三上午,發(fā)表了第一個(gè)死亡報(bào)告- 得克薩斯州一名22個(gè)月的墨西哥男嬰死亡。在墨西哥,超過(guò)150人死于被懷疑的豬流感，并有超過(guò)2,400人被懷疑受到感染.-但是只有7類死亡和26例得到實(shí)驗(yàn)室的確認(rèn)為豬流感。

但是，流感的威脅遠(yuǎn)遠(yuǎn)超過(guò)一兩個(gè)國(guó)家范圍。“我們應(yīng)該高度重視流感,因?yàn)樗�的蔓延是很快�?”世衛(wèi)組織總干事陳馮富珍說(shuō)道。“我們現(xiàn)在沒(méi)有解決辦法。但是，我們會(huì)找到的。”

隨著豬流感H1N1病毒在墨西哥和美國(guó)肆虐，并不斷出現(xiàn)在其他地方，大規(guī)模蔓延的可能性是不可避免的-因?yàn)榱鞲胁《疽子趥鞑ビ蛛y于控制。但這無(wú)法阻止衛(wèi)生官員試圖控制其擴(kuò)散的努力.周三,美國(guó)總統(tǒng)巴拉克奧巴馬表示，受影響的學(xué)校“應(yīng)認(rèn)真考慮暫時(shí)關(guān)閉，以確保我們的安全，”由于病例的確診迫使學(xué)�？紤]停課-這么做要涉及幾個(gè)州的大約50,000名學(xué)生。在周三晚上的新聞發(fā)布會(huì)上，奧巴馬還表示，“每一位美國(guó)人應(yīng)該知道，他們的政府正在采取全面的預(yù)防措施和準(zhǔn)備工作。”

有關(guān)措施包括加強(qiáng)對(duì)進(jìn)入美國(guó)游客的監(jiān)測(cè)，檢查和測(cè)試可能帶有類似流感癥狀的人，提醒仍在墨西哥的美國(guó)公民，警告他們那里的形勢(shì)似乎仍然很糟糕。與此同時(shí)，其他國(guó)家都已經(jīng)嚴(yán)格限制國(guó)民去那里旅游,意圖切斷疾病的傳播。古巴和阿根廷已暫時(shí)禁止飛機(jī)往返墨西哥，日本已經(jīng)停止向墨西哥人發(fā)放簽證.法國(guó)提出了請(qǐng)求，暫停所有往返歐洲聯(lián)盟和墨西哥的航班。

在周三的聽(tīng)證會(huì)上，國(guó)會(huì)議員尖銳質(zhì)疑國(guó)土安全部秘書珍妮納波利塔諾關(guān)于封鎖同墨西哥接壤邊界的可能性。共和黨參議員麥凱恩在一份聲明中說(shuō)： “我仍然認(rèn)為，結(jié)束這場(chǎng)危機(jī)的所有適用的選項(xiàng)都應(yīng)該予以考慮，包括關(guān)閉邊界，這么做如果能防止這種致命的病毒進(jìn)一步傳播的話。”

但是納波利塔諾說(shuō)，美國(guó)沒(méi)有計(jì)劃關(guān)閉同墨西哥接壤的邊界，這個(gè)立場(chǎng)，得到疾病控防中心（ CDC ）和世界衛(wèi)生組織的支持.也是奧巴馬在他的新聞發(fā)布會(huì)上反復(fù)強(qiáng)調(diào)的立場(chǎng)。“封鎖邊界不是防止傳染病的有效的手段,”疾病控防中心執(zhí)行主任理查德貝瑟說(shuō)道。然而，如果豬流感在墨西哥繼續(xù)惡化的話，就不難斷定奧巴馬和其他世界領(lǐng)導(dǎo)人將如何面臨越來(lái)越大的壓力，采取隔離措施-就像被感染的病人可能會(huì)被隔離，以防止該疾病的蔓延。

衛(wèi)生官員認(rèn)為，因?yàn)樨i流感H1N1病毒已在許多國(guó)家存在了，并隨時(shí)能夠人傳人，所以孤立一個(gè),兩個(gè)國(guó)家措施似乎難于奏效。雖然未被感染的國(guó)家采取嚴(yán)厲的限制國(guó)際旅行的措施,暫緩了受豬流感的影響，但是,他們不太可能能夠阻止病毒的擴(kuò)散-還有因?yàn)槁眯薪�令也給國(guó)家造成了經(jīng)濟(jì)損失,所以,這么做弊遠(yuǎn)大于利.根據(jù)布魯金斯研究所發(fā)表的一份2007年的研究報(bào)告估計(jì),航空旅行減少95%將給美國(guó)的經(jīng)濟(jì)帶來(lái)年損失1,000個(gè)億。

華盛頓大學(xué)的生物統(tǒng)計(jì)學(xué)家艾拉朗季尼說(shuō):”病毒一旦蔓延并肆虐的時(shí)候,任何旅行限制都會(huì)失效的.””與美墨之間每天4000個(gè)航班相比較,讓病毒擾亂正常的社會(huì)生活秩序是很不值得的.”

但,這并不是說(shuō)，采取非常嚴(yán)格的限制不會(huì)產(chǎn)生影響減緩病毒蔓延的。在2006年的一項(xiàng)研究中，哈佛大學(xué)流行病學(xué)家約翰布朗斯坦和肯納斯曼德?tīng)枌彶榱嗽?.11之后的流感季節(jié)里由于急劇減少空中旅行所造成的影響。他們發(fā)現(xiàn)，最初的飛行禁令和緊隨其后兩周的流感季節(jié)造成航空旅行的普遍下降并沒(méi)有減低整體的感染人數(shù)和死亡人數(shù).

由生物統(tǒng)計(jì)學(xué)家如朗季尼通過(guò)計(jì)算機(jī)模擬的情況與統(tǒng)計(jì)的數(shù)據(jù)相吻合.他發(fā)現(xiàn)即使最嚴(yán)格的限制航空旅行只會(huì)遲緩禽流感疫情的擴(kuò)散，但不會(huì)阻止其蔓延。但是，再說(shuō)一次，雖然此戰(zhàn)略只對(duì)尚未受感染的國(guó)家有利，但是還是沒(méi)有辦法知道什么時(shí)候可以安全地解除這些限制。“毫無(wú)疑問(wèn)，空中旅行傳播禽流感，”說(shuō)這番話的是曼德?tīng)?他是波士頓兒童醫(yī)院的一位醫(yī)生兼信息程序研究員以及在哈佛醫(yī)學(xué)院作副教授 “但是,由于經(jīng)濟(jì)下滑給生活帶來(lái)的影響已經(jīng)很大了,如果再限制航班,勢(shì)必會(huì)更加困難.”

就美墨邊境的問(wèn)題來(lái)說(shuō)，試圖關(guān)閉它實(shí)際上也是徒勞的.因?yàn)槊刻於加袩o(wú)數(shù)非法移民越過(guò)邊界進(jìn)入美國(guó)。任何試圖阻止偷渡的做法只會(huì)逼迫他們轉(zhuǎn)入地下,同時(shí)豬流感的傳播也進(jìn)入地下了.這將是一個(gè)頭痛的外交問(wèn)題.因此,墨西哥政府已對(duì)旅游限制表示關(guān)切了.

比較有效的辦法就是展開地方群體間隔行動(dòng)-關(guān)閉學(xué)校，要求員工在家工作，并限制公眾集會(huì),因?yàn)楣�共�?chǎng)所里禽流感容易傳播。這種方法在1918年西班牙爆發(fā)流感期間很有效果致命-其城市迅速采取行動(dòng)，在流感高峰期到來(lái)之前就關(guān)閉學(xué)校和電影院,死亡率低于行動(dòng)比較緩慢的城市的一半。今天，醫(yī)生還可以對(duì)有過(guò)密切接觸豬流感病人的人實(shí)施預(yù)防性的抗病毒藥物的治療.這種策略已被證明有助于防止禽流感擴(kuò)散. “只有你開始真正地看到大多數(shù)患者得到康復(fù)了，才可以說(shuō)這種方法真正有效. ” 朗季尼說(shuō)道。

然而，歸根結(jié)底，在這個(gè)息息相關(guān)的世界上，我們只能彼此依賴而存在.這個(gè)世界已經(jīng)變得越來(lái)越像一個(gè)整體了-正如流感病毒在國(guó)與國(guó)之間迅速蔓延一樣,“這確實(shí)是對(duì)全人類一個(gè)巨大威脅,”世衛(wèi)組織的陳說(shuō)道。無(wú)論將來(lái)會(huì)發(fā)生什么-我們會(huì)在一起。