H7N9 and the skewed age issue.

We are reading much about the older than expected ages of those infected by H7N9 (current average case age of 58 years). Why? One school of thought is that the elderly have weaker, or perhaps "less experienced" immune defences. 

But there are many other risk factors for severe complications arising after influenzavirus infection including heart and other organ disease, things which may accumulate with age.

This shift is not uncommon among pandemic influenzaviruses - those settling in to a new host. Also worth noting: (1) seasonal influenza is commonly regarded as having its worst impact in those over 65 years of age, (2) influenza A(H5N1) virus (the other bird flu) has had its biggest impact in pre-adults and young adults (15-39)(3) the influenza A(H1N1)pdm virus (swine flu) had its greatest impact on children and young adults and(4) influenza A(H7N7) virus was confirmed in 89 people (average age 30 years among mostly workers culling chickens), mostly mild, including conjunctivitis.

That' a lot of diversity. Begs the question of whether we can predict too much about H7N9 until we've lived with it a bit longer.