Over 60s immune from Swine Flu

Friday, 19 June 2009

This week the World Health Organisation (WHO) have officially declared the outbreak of swine flu to be a pandemic. The epidemic has now hit 74 countries with the mortality rate 141 deaths out of 30,000 cases, a similar rate to normal flu.

However, at the same time health protection agencies and doctors have noticed that over 60s appear to be immune to swine flu, according to the Daily Mail. In fact, it is actually young people who are the most vulnerable. As Dr Keiji Fukuda of the WHO said: "The bulk of cases are among younger people - mainly in their 20s."

It is necessary to understand that viruses change and evolve as they circulate in the human population. The reason for younger people's greater susceptibility seems to be that they have not had sufficient time to build up immunity from this virus as have the older population. Once a person has developed immunity to a virus, by making antibodies to it in their blood, they usually retain this for the rest of their life. Hence the thinking behind vaccination.

So why are older people immune to swine flu? The reason may be its very name, H1N1 which means it is formed from two components H1 and N1.

The H1 component formed part of the virus which was spreading during the flu pandemics of 1918 and 1957. People alive during this period would have developed antibodies and therefore lifelong immunity to the H1 component.

However, after 1957, the H1 component of flu evolved. New viruses resulted which were unable to be recognised by the original H1 antibodies. This meant that the whole population became vulnerable to the new flu viruses.

The reason why over 60s have an immunity to swine flu is that the virus has not mutated very much in pigs and still resembles the early H1 from the 50s. Swine flu contains the original H1 so older people are immune and younger people who have not built up resistance are at risk from infection.

This winter should see fewer complications among flu sufferers as the strain is likely to be swine flu. sufferers will be younger people who are less likely than over 60s to develop pneumonia. Hopefully therefore there should be a lower death rates from any epidemics this year.

Over 60s should continue to receive their regular flu jab as usual, to reduce risk of contracting the more common kinds of flu.

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