Researchers from the MRC Centre for Outbreak Analysis and Modelling at Imperial College London, working in collaboration with the World Health Organization and public health agencies in Mexico, have assessed the threat presented by the new strain of influenza A (H1N1) in Mexico.
The researchers estimate 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. The researchers stress that healthcare has greatly improved in most countries since 1957 and the world is now better prepared. The epidemic of influenza A (H1N1) is thought to have started in Mexico on 15 February 2009. The data, published in Science magazine, 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. However, the figures are uncertain as some mild cases may have gone unreported. For every person infected, it is likely that there will be between 1.2 and 1.6 secondary cases. This is high compared to normal seasonal influenza, where around 10-15% of the population are likely to become infected. However, it is lower than would be expected for pandemic influenza, where 20-30% of the population are likely to become infected. Professor Neil Ferguson, author of the research, said: “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. “What we’re seeing is not the same as seasonal flu and there is still cause for concern – we would expect this pandemic to at least double the burden on our healthcare systems. However, this initial modelling suggests that the H1N1 virus is not as easily transmitted or as lethal as that found in the flu pandemic in 1918,” added Prof. Ferguson.
