Pandemic May Be Over But H1N1 Flu Virus Could Remain a Threat

Researchers say that although the World Health Organization (WHO) has declared that the H1N1 pandemic is over, it does not mean that this influenza virus no longer poses a health threat.

Stephen J. Turner, of the Department of Microbiology and Immunology at the University of Melbourne in Melbourne, Australia, Peter C. Doherty of the Department of Immunology at St Jude Children's Research Hospital in Memphis, Tenn., and Anne Kelso, of the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne, Australia, explain what it means for the World Health Organization to have announced the end of the (H1N1) influenza A (H1N1) pandemic: "In 2009, the new H1N1 pandemic virus exhibited several features that distinguished it from seasonal influenza: it caused major outbreaks in the northern hemisphere summer and autumn, it quickly dominated over other influenza viruses circulating in humans, and it caused widespread disease because of the lack of significant population immunity, particularly in young people. In 2010, the pandemic virus is behaving more like a seasonal influenza virus in that summer outbreaks have not been seen, it is co-circulating with seasonal A(H3N2) and B viruses, and the intensity of transmission is now lower than in 2009. For these reasons, WHO downgraded its pandemic alert from phase 6 to the post-pandemic phase on 10 August 2010. Fortunately, in contrast to descriptions of the 1918 Spanish influenza pandemic, there has been no apparent change in disease severity over the first 18 months of circulation of this virus."

The researchers say that several features of the pandemic H1N1 influenza virus are a continued cause for concern, as they point out, "for example, most hospitalizations and deaths are still in those under 60 years old. This is probably because people in this age group are less likely to be immune. Furthermore, of those people admitted to hospital in the U.S. with confirmed influenza (H1N1) 2009 pneumonia, almost two-thirds end up in intensive care. Recent clinical studies have identified risk factors for severe disease that include, but are not limited to, obesity, cardiovascular disease and pregnancy. Importantly, however, about one-third of those who have died with (H1N1) 2009 lacked any known risk factors. It is also of concern that the human influenza (H1N1) 2009 virus can be found in limited instances within pig populations, the species from which it emerged. This increases the opportunity for the virus to reassort with other avian and swine viruses to produce new influenza strains of unpredictable transmissibility and virulence."

To read a Q&A from Turner, et al. (2010) in BMC Biology, CLICK HERE.

Reference: Turner SJ, Doherty PC and Kelso A. Q&A: H1N1 pandemic influenza - what's new? BMC Biology 2010, 8:130doi:10.1186/1741-7007-8-130