# 440
Amongst flu watchers, and on flu forums, one of the most hotly debated subjects over the past year or so has been the age distribution of the victims of the H5N1 virus. This is a phenomenon we've discussed on this blog many times. The last time was in The Riddle of the Ages, on Dec 4th.
The virus, thus far, strikes those under the age of 40 roughly 90% of the time. 52% of all victims are under the age of 20.
This from CBC news
90% of bird flu cases hit people under age 40: WHO
Last Updated: Saturday, February 10, 2007 | 8:52 PM ET
CBC News
Nearly 90 per cent of the people who have been diagnosed so far with H5N1 strain of the avian flu virus were under age 40, a new analysis from the World Health Organization shows.
And two British scientists suggest that as yet unexplained phenomenon could be a clue that widespread immunity to infection with the virus may exist in people aged 35 and older.
The age distribution of H5N1 human cases is "consistent with a biological model of geographically widespread immunity to avian influenza A (H5N1) in persons born before 1969," Matthew Smallman-Raynor of the University of Nottingham and Andrew Cliff of the University of Cambridge note in a letter to the March issue of the journal Emerging Infectious Diseases.They said such a model would account for:
- The similar rates of disease in younger people.
- The "sudden and pronounced reduction" of cases in patients over age 30-35.
- The age skew that "transcends the sociocultural and demographic contexts of countries and continents."
The idea is, put simply, that some (as yet unidentified) influenza virus circulated the globe in the 1960's and conferred immunity to the H5N1 virus to those of us born before 1969.
This theory is not unlike the explanation sometimes given for the reduction in flu deaths seen during the Spanish Flu among those aged 65 and older. The assumption there is, sometime in the mid 1800's, another influenza virus may have inoculated the population.
But it is just an assumption.
Obviously, this phenomenon deserves more study. It is, as I've pointed out many times, a riddle. A scientific mystery. And solving it might give us valuable answers as to how to treat, or even prevent infection.
As to whether these researchers, Smallman-Raynor and Cliff, who teach analytical and theoretical geography, have deduced the solution; it is premature to say. It would require that a mild form of a similar virus to have swept the world in the 1960's, and for scientists not to have noticed.
Possible, I suppose. Surveillance and testing has improved a good deal in 40 years.
So I shall keep this, along with a half dozen other theories, in the `It's possible' stack, admit I haven't a clue, and wait for smarter people than I to figure it out.
