As discussed in a post five months ago[1] the prospect for the current (2012/13) influenza season was always debatable. However I am pleased to say that my prediction that there was “no real grounds for suggesting a severe season in the coming winter” has turned out to be right. Although there has been increased activity when compared to last year, the latest HPA numbers[2], which records cases seen by GPs and recorded as possible flu (ILI – influenza like illness) and those that go to the lab and are confirmed as flu, are very modest this year and appear as a blip when compared to years of high virus circulation like 1999 and 2010. As the graph shows (left panel), the season is now effectively over so we can assume we have escaped a severe bout of influenza for another year. The reasons for a low incident year are as unclear this year as there were last.

The viruses that did circulate (right panel) were, in the main, influenza B and influenza A H3 subtype (one of the longstanding seasonal influenza strains). The “swine flu” now known as pandemic H1N1 (pdm09) which caused the 2009 pandemic is still around but at a low level and the previous H1N1 seasonal influenza, which emerged in 1977, appears to have disappeared. Curiously the healthcare and hygiene company Reckitt Benckiser reported a good financial return for the last year boosted in part by strong demand in the last quarter for cold and flu treatments.[3]  Whatever respiratory viruses were circulating (there are ~ 6 different viruses whose effects are similar and all peak in the winter months) it was clearly not influenza as even in the US most states witnessed a moderate or low level of activity.[4]

As discussed in my norovirus post,[5] the algorithm for flu strain circulation (which strain and to what level) is complicated and cannot yet be accurately modelled meaning that long term planning for influenza outbreaks remains essentially guesswork.