‘‘Even if you erred on the side of caution and estimated that one million people got it, and that one in every 1,000 of those people were to die, it is like four jets going down in Dublin airport.”

That statistic comes from someone who should know; Professor Sam McConkey, head of the Department of International Health and Tropical Medicine at the Royal College of Surgeons in Ireland (RCSI).

McConkey was talking about the effects of H1N1 flu - or swine flu - which is expected to affect between 20 and 40 percent of the population of the Republic of Ireland.

The figures, which are from the European Center for Disease Control, could see up to 1 million people coming down with the flu in Ireland.

There have been 226 cases of human swine flu confirmed in Ireland and one man is critically ill in St James Hospital with the virus.

The man, from Bratislava in Slovakia, was taken into hospital late last week. It is believed that he contracted the virus outside Ireland.

So far, health authorities say there have been just 32 cases of person-to-person transmission in Ireland. Worldwide, there have been 134,503 reported confirmed cases of human swine flu and 816 deaths.

In the U.S. the death toll so far averages out at one death per 300 reported cases. In Britain the toll is much lower; one in every 500.

However, health officials say it is difficult to estimate any type of death toll because the numbers only include the reported cases.

Tens of thousands of people in Ireland and the U.S are believed to have been infected with a mild case of the virus but shrugged it off as a cold or light flu.

However, Ireland is preparing to cope with a major outbreak in the country and doctors have already been warned to take every precaution.

Dr Tony Holohan, the chief medical officer at the Department of Health, has predicted that Ireland will see about 1 million cases of the virus in the fall and winter, or about 25 percent of the population.

This would stretch the country's medical resources to its limit.

McConkley says the high figures show there is little immunity to the flu because, he says,  it is a new strand and is highly contagious.

"Most people appear to not be immune to the virus,”  said McConkey, “The second point is that this influenza, while it is not particularly severe in many cases, does appear to be quite infectious.”

McConkey admits that experts do not how the H1N1 pandemic strain formed and described it as "effectively a hodgepodge of different viruses."

But McConkey had some encouraging news for Ireland. He said that the number of cases in Ireland was actually far lower per head of population in comparison to the U.S. and Britain (the British government has itself forecast that there could be as many as 100,000 new cases per day in the coming weeks and 20-30 percent of the population there could also come down with swine flu.

“What we can say with some degree of certainty is that seasonal influenza is much more common in Ireland circulates from October to March and it doesn’t really circulate in June July and August, it disappears and goes elsewhere," he said.

“People’s mixing patterns are different in different in wintertime than in summertime, there are a lot more people coming together in groups in schools in winter activities, whereas in summer people go off on holidays,” he said.

“It may also be the weather; the weather is colder and there is a higher humidity, there are other climactic factors that may influence the transmission as well the social mixing patterns, but I believe it is really fair to say that we don’t know with any degree of confidence which exact factors it is contribute to the higher degree of the spread of flu in wintertime.”