Has the impact of H1N1 flu changed?
The prevalence of severe cases of H1N1 is four times greater than at the peak in 2009 but has their age-distribution altered?
Those who want to follow closely what’s happening with England’s third wave of swine-flu have to look at both the '"interwatch" report published on the DH website and at weekly figures on flu and flu-like illness published on a Thursday afternoon by the Health Protection Agency via its weekly flu report. Their latest report is here.
Now I have located minimal key data by age-group on the prevalent number of patients with suspect or confirmed influenza and in critical care beds, it is possible to compare the impact of the three waves of H1N1. The Table shows the peak-ICU-week for the first and second waves of swine-flu in 2009 and, for 2010, shows the week in which England matched its second wave peak (15 December) and two weeks later by which time prevalent cases in critical care had quadrupled.
The key finding is the broadly stable age-pattern for cases in critical care across the three waves of H1N1.
Currently, there is no reporting of England’s prevalent numbers of patients hospitalized for suspect swine-flu (or influenza). Presumably this is because of unresolved genuine concern that the available data for the first two waves in England were not comparable.
The reasons are plain to see – whereas 2009’s numbers in critical care doubled between the first and second peak-ICU-peak, prevalent hospitalizations were equal but differed in their age-pattern. If the later hospitalization figures for 18 November 2009 were the more reliable, then we might assume that the ratio of in-critical care to in-hospital could be around 1:10 for the under-5s and 5-15 year olds but 1:3 for 16-64 year olds and 1:6 at 65+ years of age in mid-November 2009. However, 18 November 2009 was still mainly pre-H1N1-immunization.