The swine flu virus will infect a third of the world's population if it continues to spread at its current rate, scientists warned today, as three more cases were confirmed in the UK.

In what the journal Science described as the "first quick and dirty analysis" of swine flu, a study by researchers at Imperial College London predicted the virus was likely to cause an epidemic in the northern hemisphere in the autumn.

One of the authors, the epidemiologist and disease modeller Neil Ferguson, who sits on the World Health Organisation's emergency committee for the outbreak, said the virus had "full pandemic potential".

Speaking on BBC Radio 4's Today programme, he said: "It is likely to spread around the world in the next six to nine months, and when it does so, it will affect about one-third of the world's population.

"To put that into context, normal seasonal flu probably affects around 10% of the world's population every year, so we are heading for a flu season which is perhaps three times worse than usual – not allowing for whether this virus is more severe than normal seasonal flu viruses."

The Health Protection Agency announced three more confirmed cases of the virus in the UK, bringing the total to 68. The three patients – two children and one adult from London – all had close contact with previously confirmed cases.

Today's study estimated the contagiousness of the disease by analysing the number of people travelling to Mexico who became infected, and comparing that with a study of a Mexican village where the disease has spread. The research also examined how the virus was mutating.

It estimated that swine flu had killed between 0.4% and 1.4% of its victims in Mexico. The report's lead author, Christophe Fraser, said it was too early to predict what the death rate was likely to be outside Mexico. "My hunch is that the death rate will be lower elsewhere – Mexico has underlying issues with respiratory disease," he said.

The researchers said this H1N1 virus appeared to be about equal in severity to the flu of 1957, and less severe than the deadly 1918 version.

"At the moment the virus is not spreading fast in the northern hemisphere because we are outside the normal flu season, but come the autumn it is likely to cause a really major epidemic," Ferguson said.

He declined to put an estimate on the number of deaths that may occur. "We have some assessment, but the uncertainty is still quite broad," he said.

"We can say it is not going to be as catastrophic as the Spanish flu pandemic of 1918, it is milder than that. But it is still possible it could be [like] 1957 – where about three to four out of 1,000 people who were infected died and overall about 3 million to 4 million people died that year because of the pandemic worldwide – or it could be even milder than that, like the 1968 pandemic which was barely worse than a normal seasonal flu year.

"I am not predicting three million to four million [deaths]. That was what happened in 1957. The world is a very different place today. There are more people in the world, but there is also a much better healthcare system. We have drugs and vaccines, particularly in developed countries, which should markedly reduce the burdens of the disease."

Ferguson said the findings of the study confirmed that decisions must be taken swiftly on vaccine production.

"One of the key decisions which has to be made this week by the world community is how much do we switch over current vaccine production for seasonal flu to make a vaccine against this particular virus."

Today Cuba and Thailand confirmed their first case of the virus. The patient in Cuba is a Mexican student at a medical school.

Fidel Castro accused Mexico of failing to disclose the spread of swine flu until after Barack Obama, the US president, had visited the country on 16 April. In a newspaper column, the former Cuban leader wrote: "Mexican authorities did not inform the world of the presence [of swine flu], while they waited for Obama's visit."

At least 61 people have been killed by swine flu around the world, and the WHO has confirmed about 4,800 cases.

今天，英國又確診了三例豬流感病例，科學家們警告說，如果豬流感繼續以現在的速度傳播，它將會最終影響全世界三分之一的人口。

在倫敦帝國學院的調查人員所進行的被《科學日報》稱為“第一次快速分析豬流感”的研究中，科學家預測，該病毒今年秋天可能在整個北半球形成大流行。

調查報告的作者之一、世界健康組織突發疾病委員會成員、流行病學專家及疾病模型專家尼爾.弗格森說，這種病毒具有“大流行的全部潛質”。

在BBC電臺的《今日》節目中，他說：“豬流感可能會在接下來的六至九個月內傳至全世界，如果真的如此，那它將影響全球近三分之一的人口。”

“相比之下，一般的季節性流感每年只影響全球十分之一人口，因此，今年我們所面臨的是一個比正常年份可能槽糕三倍的流感季節----而且還沒有考慮是否這種病毒會比正常的季節性流感病毒更難對付。”

繼健康防護署又宣布增加三例新的豬流感確診病例后，英國的確診人數達到了68人。這三例新的病例----來自倫敦的兩名兒童和一名成人----都與前面已確診的病人有過密切接觸。

今天的研究通過對在墨西哥旅游而受到感染的人數的分析，再對比墨西哥一個村莊疾病傳播的研究，對該病毒的接觸傳染力進行了估計。調查還分析了病毒是如何進行變異的。

據估計，豬流感的死亡率在墨西哥的感染者中已經達到了0.4%至1.4%。調查報告的主要作者克里斯托夫.弗雷澤說，現在預測墨西哥以外地區的死亡率還為時太早，“我覺得其它地方的死亡率會比墨西哥小，因為墨西哥對呼吸道傳染疾病的處理有些問題。”他說。

調查人員說，這次的N1H1病毒的嚴重程度看起來與1957年的流感差不多，但比1918年的致命的流感病毒要輕。

“目前病毒還沒有在北半球傳播得很快，是因為我們還沒有到通常的流感季節，但一到秋季，它就很可能會引起一場真正大范圍的流行病。”弗格森說。

他拒絕對可能出現的死亡人數進行估計，“我們有一些評估，但是不確定性還是太多。”他說。

“我們可以說，它不會成為象1918年西班牙流感大流行那樣的災難，它要溫和一些，但是仍然有可能會象1957年的那場流感一樣----那場流感中，千分之三至四的人口受到感染而死，病毒在全世界范圍內傳播流行，在那年導致了全球三百至四百萬人口死亡----或者，它也可能比57年的流感更輕微，就象1968年一樣，那次流感只是比每年的正常季節性流感稍微嚴重些。”

“我不會預測將有三百到四百萬的死亡人數，那是發生在1957年的事，而今天的世界已經跟那時候大大不同了。世界的人口增多了，但是衛生保健系統也好得多了。我們有了藥物和疫苗，特別是在發達國家，所以可以顯著減少疾病導致的嚴重后果。”

弗格森認為，這次研究的發現表明，必須立即下決心進行疫苗生產。

“這個星期中世界各政府必須作出的關鍵決定之一，就是我們應該將多少目前用于季節性流感疫苗的生產力轉向到生產對付這一特殊病毒的疫苗。”

今天，古巴和泰國也確診了他們的首例豬流感病例。古巴的病例是一名在醫學院上學的墨西哥學生。

菲德爾.卡斯特羅指責墨西哥直到美國總統奧巴馬4月16日訪墨后才公布了豬流感傳播的信息。在一份報紙的專欄中，這位古巴前領導人寫道：“墨西哥當局沒有向世界通報豬流感蔓延的現實，因為他們要等待奧巴馬的來訪。”

全世界已經有至少61人死于豬流感，世界衛生組織已經證實有約4800例確診病例。