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Paradigm Shift Intervention Monitoring
Experience during the 2010–2011
influenza season in the northern hemisphere has demonstrated that
pandemic influenza A(H1N1) 2009 virus is still circulating and,
importantly, still causing severe disease in younger people. Continued
vigilance is imperative, and the appropriate surveillance, control and
treatment practices that allow for the control of both established
seasonal influenza strains and pandemic influenza A(H1N1) 2009 virus
should be maintained during the post-pandemic period.
The above warning represents the WHO conclusions in the report, “Influenza A(H1N1) 2009 virus: current situation and post-pandemic recommendations” in today’s Weekly Epidemiological record. It follows the August declaration that the H1N1 pandemic phase had ended. At the time H1N1 was widespread in India as well as multiple countries in the southern hemisphere and was killing previously healthy young adults. The recent outbreak in the UK indicated that H1N1 levels were higher than last season, leading to a spike in ICU cases as well as saturation in use of ECMO machines which had increased four fold over levels in the prior season.
Sequence data from UK isolates indicated November isolates were dominated by two sub-clades with S186P or S188T. These sub-clades began to emerge and spread in the southern hemisphere and had become dominant in the UK. Similar sequences were subsequently reported throughout the northern hemisphere, including the United States and Canada in North America, as well as Mongolia, Russia, China, and Japan in Asia. In the US the week 4 P&I death rate spiked to 8.45% and week 6 spiked to 8.89%, just shy of the five year high of 9.1% in week 11 in 2008. This dominance and spread suggests outbreaks similar to the UK will be widespread throughout the northern hemisphere in the upcoming weeks.
The above data supported vaccine escape, which was confirmed by a 50% failure rate in the UK. However, in spite of these dramatic results, the WHO advisory committee recommended the same vaccine targets for the 2011/2012 season, raising serious concerns about the utility of the antigen characterization tests which produced intra and inter-lab variations including results inconsistent with sequence and clinical data (discussed in detail here).
The WHO warning on the emerging H1N1 sub-clades is appropriate, but recommendations for vaccination using targets which produced poor protection against contemporary sub-clades continues to raise serious concerns about the current vaccine target selection and strategy.