First assessment of A H1N1) v risks published in the Science magazine
Researchers from the MRC Centre for Outbreak Analysis and Modelling at Imperial College London, led by Professor Neil Ferguson, working in collaboration with the World Health Organisation and public health agencies in Mexico have assessed the novel A H1N1 influenza using data to the end of April. The results of this study were published in the Science magazine. 
It seems that the new strain of H1N1 acts more like a pandemic strain than regular seasonal flu. The researchers' best estimate is that in Mexico influenza A (H1N1) is fatal in around 4 in 1,000 cases, which would make this strain of influenza as lethal as the one found in the 1957 pandemic.
Transmissibility is substantially higher and affects young adults more often than seasonal flu. These data justify the decision of the World Health Organisation to raise the worldwide pandemic alert level to Phase 5, one step down from a full pandemic.
The article is available online: Full text Pdf version