Swine flu that has triggered global health scare has "full pandemic potential" and is fatal in around 4 in 1,000 cases making this strain of influenza as lethal as the one found in the 1957 pandemic, research by British scientists reveals.

The first detailed analysis by researchers at London's Imperial College, found that the virus spreads easily from person to person infecting around one in three of those who come into contact with it.

Professor Neil Ferguson the author of the research said it was too early to say whether the virus will cause deaths on a massive scale, or prove little more lethal than normal seasonal flu.

"Our study shows that this virus is spreading just as we would expect for the early stages of a flu pandemic. So far, it has been following a very similar pattern to the flu pandemic in 1957, in terms of the proportion of people who are becoming infected and the percentage of potentially fatal cases that we are seeing", said Ferguson.

"Swine flu is certainly milder than the Spanish flu which caused an estimated 50 million deaths in 1918, but it is not yet possible to say whether it will kill more than the most recent pandemics in 1957 and 1968", he said.

The epidemic of influenza A (H1N1) is thought to have started in Mexico on 15 February 2009. The data published in the journal Science suggests that by the end of April, around 23,000 people were infected with the virus in Mexico and 91 of these died as a result of infection.

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