There are signs of a decline in seasonal flu. But the quest for a vaccine remains as important as ever

There remains the threat that a mutated strain could cause a global pandemic

Like the first daffodils, the first swifts and the first bonfires, the annual flu outbreak marks the passing of the seasons. So the news that this most cyclical of eruptions may be in terminal decline comes with no shortage of implications. This winter’s GP consultation rates are running at a 10th of the normal level – 3.1 per 100,000 of the population, according to the latest official figures. On present trends, barring last-minute surprises, this will be the lowest flu season on record, continuing the virus’s 40-year decline.

For most of us, flu is nothing more serious than a few days on the sofa with the latest box-set. But it is also a killer, carrying off thousands of mostly elderly people every year. And among younger people, especially children, it can cause high fever, requiring hospitalisation, and lead to later complications such as ear infections. While most healthy people can see it off with a hot drink and a dose of paracetamol, it is not a virus to be trifled with.

There is also its apparently endless capacity for mutation to consider. The swine flu pandemic of 2009, though less severe than expected, nonetheless claimed more than 1,000 lives in the winters of 2009-10 and 2010-11, among them pregnant women. Now, a new lethal strain with a high death rate has emerged in China – H7N9 – causing widespread alarm. So far all recorded cases – 355, including 67 deaths – have been linked with exposure to poultry and there is no evidence of sustained human-to-human transmission which could trigger a new global pandemic. But the threat is real and the need for vigilance constant. So, too, is the need for a flu vaccine that provides effective, long-term protection for all age groups against all strains of the virus – still a distant dream.

As things currently stand, flu vaccines have to be re-formulated every year on the basis of an educated guess by scientists who attempt to match it with the strains of the virus likely to be circulating that season. The whole process has to be repeated the following year.

And because the virus mutates rapidly, the scientists don’t always get it right. The vaccine made for the winter of 2011-12 was a particularly poor match – researchers estimated it shortened the illness by half a day but did not reduce the number of people hospitalised. But, even in a good year, the vaccine provides limited protection, perhaps around 60 per cent in healthy adults and half that in the over-65s. Yet public-health experts say even at these low levels it is worth doing.

In England, plans are under way to extend the annual flu vaccination from over-65s, pregnant women and the chronically sick, to all school-age children, who are thought to be the main spreaders of the virus. If successful, that is likely to reduce the impact of the winter flu still further. That should be a cause for celebration. But the threat from a mutated strain causing a global pandemic will remain.

While the demise of seasonal flu can only be welcome, then, we should not forget the power of this simple virus to wreak havoc on a global scale. And we can only urge the vaccine industry to redouble its efforts in the search for a more reliable defence against it.