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，英国又确诊了三例猪流感病例，科学家们警告说，如果猪流感继续以现在的速度传播，它将会最终影响全世界三分之一的人口。

在伦敦帝国学院的调查人员所进行的被《科学日报》称为“第一次快速分析猪流感”的研究中，科学家预测，该病毒今年秋天可能在整个北半球形成大流行。

调查报告的作者之一、世界健康组织突发疾病委员会成员、流行病学专家及疾病模型专家尼尔.弗格森说，这种病毒具有“大流行的全部潜质”。

在BBC电台的《今日》节目中，他说：“猪流感可能会在接下来的六至九个月内传至全世界，如果真的如此，那它将影响全球近三分之一的人口。”

“相比之下，一般的季节性流感每年只影响全球十分之一人口，因此，今年我们所面临的是一个比正常年份可能槽糕三倍的流感季节----而且还没有考虑是否这种病毒会比正常的季节性流感病毒更难对付。”

继健康防护署又宣布增加三例新的猪流感确诊病例后，英国的确诊人数达到了68人。这三例新的病例----来自伦敦的两名儿童和一名成人----都与前面已确诊的病人有过密切接触。

今天的研究通过对在墨西哥旅游而受到感染的人数的分析，再对比墨西哥一个村庄疾病传播的研究，对该病毒的接触传染力进行了估计。调查还分析了病毒是如何进行变异的。

据估计，猪流感的死亡率在墨西哥的感染者中已经达到了0.4%至1.4%。调查报告的主要作者克里斯托夫.弗雷泽说，现在预测墨西哥以外地区的死亡率还为时太早，“我觉得其它地方的死亡率会比墨西哥小，因为墨西哥对呼吸道传染疾病的处理有些问题。”他说。

调查人员说，这次的N1H1病毒的严重程度看起来与1957年的流感差不多，但比1918年的致命的流感病毒要轻。

“目前病毒还没有在北半球传播得很快，是因为我们还没有到通常的流感季节，但一到秋季，它就很可能会引起一场真正大范围的流行病。”弗格森说。

他拒绝对可能出现的死亡人数进行估计，“我们有一些评估，但是不确定性还是太多。”他说。

“我们可以说，它不会成为象1918年西班牙流感大流行那样的灾难，它要温和一些，但是仍然有可能会象1957年的那场流感一样----那场流感中，千分之三至四的人口受到感染而死，病毒在全世界范围内传播流行，在那年导致了全球三百至四百万人口死亡----或者，它也可能比57年的流感更轻微，就象1968年一样，那次流感只是比每年的正常季节性流感稍微严重些。”

“我不会预测将有三百到四百万的死亡人数，那是发生在1957年的事，而今天的世界已经跟那时候大大不同了。世界的人口增多了，但是卫生保健系统也好得多了。我们有了药物和疫苗，特别是在发达国家，所以可以显著减少疾病导致的严重后果。”

弗格森认为，这次研究的发现表明，必须立即下决心进行疫苗生产。

“这个星期中世界各政府必须作出的关键决定之一，就是我们应该将多少目前用于季节性流感疫苗的生产力转向到生产对付这一特殊病毒的疫苗。”

今天，古巴和泰国也确诊了他们的首例猪流感病例。古巴的病例是一名在医学院上学的墨西哥学生。

菲德尔.卡斯特罗指责墨西哥直到美国总统奥巴马4月16日访墨后才公布了猪流感传播的信息。在一份报纸的专栏中，这位古巴前领导人写道：“墨西哥当局没有向世界通报猪流感蔓延的现实，因为他们要等待奥巴马的来访。”

全世界已经有至少61人死于猪流感，世界卫生组织已经证实有约4800例确诊病例。