Understanding H1N1 Influenza
Friday, June 12th, 2009
BBC Medical Science — Fergus Walsh reports: Do you want to avoid catching H1N1 swine flu? … You could find a remote, uninhabited island until a vaccine is created. I think that’s going a bit far. But the best defence is age.
So far, the over-65s has been the group least likely to catch the infection. This has led to me receiving cheery comments from retired people saying that it’s the first time in some while that they’ve felt glad to be old.
So why aren’t they falling ill? The likeliest explanation is that they have built up immunity over years of exposure to other H1N1 flu viruses. That might also help to explain why most other people get a mild infection.
But I’m still puzzled as to why 30- to 50-year-olds are suffering a disproportionate amount of severe illness. In fact, I’m a bit puzzled as to exactly which age groups - under the age of 65 - are most at risk of severe illness.
In her speech in Geneva yesterday, Margaret Chan, the WHO director-general, had this to say:
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“In some of these countries, around 2% of cases have developed severe illness, often with very rapid progression to life-threatening pneumonia. Most cases of severe and fatal infections have been in adults between the ages of 30 and 50 years. This pattern is significantly different from that seen during epidemics of seasonal influenza, when most deaths occur in frail elderly people. Many, though not all, severe cases have occurred in people with underlying chronic conditions.
“Based on limited, preliminary data, conditions most frequently seen include respiratory diseases, notably asthma, cardiovascular disease, diabetes, autoimmune disorders, and obesity.
“At the same time, it is important to note that around one third to half of the severe and fatal infections are occurring in previously healthy young and middle-aged people. Without question, pregnant women are at increased risk of complications. This heightened risk takes on added importance for a virus, like this one, that preferentially infects younger age groups.” (06/12/09)



