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Why it pays to be old

Fergus Walsh | 15:08 UK time, Friday, 12 June 2009

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.

margaret chanSo 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:

"We know that the novel H1N1 virus preferentially infects younger people. In nearly all areas with large and sustained outbreaks, the majority of cases have occurred in people under the age of 25 years.
"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."

This was very similar - up to a point - to the briefing yesterday by the CDC in Atlanta. You'll notice the same emphasis on younger age groups, pregnant women and those with underlying health problems. This is what Dr Anne Schuchat had to say about the US experience of H1N1 swine flu:

"It is a very new virus. 57% of the cases that we're having reported to us occur in people five to 24 years of age, and 41% of the hospitalisations are in that same age group - the older children and young adults. But I also want to tell you about the rates, the cases per 100,000 population, and let you know that the highest rates of hospitalization are actually in children under five. And the next highest rates are in those people 5 to 24. So it looks like this is a virus that's disproportionately affecting younger people but there are still lots of infections and hospitalizations in older persons.
"According to the US statistics, 71% of the hospitalized patients have occurred in people who have an underlying condition - respiratory illness like asthma or conic obstructive pulmonary disease, immune deficiencies, and so forth. As we have noted, there's been a disproportionate amount of pregnant women among those who have had infection."

Did you spot the difference? Dr Schuchat made no direct mention of the 30-50 age group, although she did mention that there were lots of people over 24 who are taken to hospital. If the 30-50 year group is especially at risk, it would be good to know. I'm still just in that age group myself, so maybe it's self-interest at work here. No doubt all will become clearer in the months ahead. When it does, I will let you know.

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