The new pandemic influenza A/(H1N1)pdm09 virus: is it really "€œnew"?




In June 2009 the World Health Organization (WHO) issued a pandemic alert concerning the spread of an influenza A (H1N1) virus showing distinctive genetic characteristics vis-à-vis both seasonal influenza strains and vaccine strains. The most relevant mutation occurred in the hemagglutinin (HA). Mathematical models were developed to calculate the virusâs transmissibility and the results indicate a significant overlap with the transmissibility of previous pandemic strains and seasonal strains. The remarkable feature of A/(H1N1)pdm09, compared with seasonal strains, is the high related fatality rate and its higher incidence among younger people. Data provided by the WHO on the number of deaths caused by A/(H1N1)pdm09 only include laboratory-confirmed cases. Some authors suggest that these data underestimate the magnitude of the event because laboratory confirmation is not obtained in all cases. It is important to bear in mind that the A/(H1N1)pdm09 virus is still circulating in the population, making it essential to keep its epidemiological and virological surveillance in place.


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