Swine flu: A health warning

When my children were small they used to beg me to tell them the story of the boy who cried wolf. The little ghouls loved the denouement when the wolf "ate all the people up".

I was happy to keep telling it too, watching their rapt faces, because it contained a moral that it seemed important to pass on: even when liars tell the truth, they are never believed.

Now I and my colleagues in the media are the ones accused of crying wolf. A groundswell of opinion is growing that the swine flu "pandemic" has been hyped by newspapers and broadcasters eager for a scare story that boosts revenues, and by scientists sensing where their next research grant is coming from.

Yesterday, as Graeme Paccitti, a 24-year-old NHS worker at Falkirk Royal Infirmary, was confirmed as Britain's first case of human-to-human contact in this country, scientists appeared to lend support to the sceptics' case by announcing that initial analysis of the H1N1 swine flu virus conducted at the National Institute for Medical Research in north London suggested it was similar to H1N1 seasonal flu and there was no immediate cause for concern. But then they spoilt things for the doubters by observing that even a mild virus can kill on a frightening scale, if enough people are infected.

The 1957 pandemic had only a 0.1 per death rate but because it infected 30 to 70 per cent of the population it killed two million people worldwide. Seasonal flu infects up to 6 per cent of the population in an average year.

It is often said, only half in jest, that there are only two kinds of medical story: the deadly scare and the miracle cure. The first task of the medical reporter, a role I have filled for more than 20 years, is to distinguish the two (not as easy as it sounds) and assess how deadly or miraculous each story is. Like many colleagues, I have made myself unpopular with newsdesks by playing scares down – the supposed link between the MMR vaccine and autism is one that springs to mind.

But not this time. The pandemic threat posed by this H1N1 swine flu virus is real for one fundamental reason that some sceptics have ignored. This is a wholly novel flu virus, of a kind that has not been seen for a generation.

It has happened as a result of the mixing of pig, bird and human flu viruses and that hybrid has jumped the species barrier and begun transmitting from human to human. As it is a novel virus, immunity to it is likely to be low or non-existent. That is a new and disturbing development. How disturbing? It is too early to say. Right now the risk is low. The only health advice I gave my children (one returned three weeks ago from Mexico City and the other is touring the US) still holds good – don't smoke and be careful crossing the road. Nothing else is worth worrying about.

But what of the next weeks, months, maybe years? Flu is a highly infectious disease. In today's globalised world, linked by air travel, it has spread to a dozen countries in as many days. The US, Germany, Spain and now the UK have reported transmission within their countries and all medical authorities agree the number infected will increase.

What we don't know is how far it will spread, how severe it will be or how long any pandemic would last.

If the early encouraging findings from analysis of the virus are confirmed, one possible scenario is a pandemic of mild illness that causes deaths on a scale not dissimilar to seasonal flu. "Pandemic" refers to the transmissibility of the virus, meaning "sustained human transmission within more than one country in separate WHO [World Health Organisation] regions". It does not inevitably mean Armageddon.

On the other hand, the more widely the virus spreads, even if mild, the more deaths it is likely to cause. Seasonal flu causes 4,000 to 12,000 deaths each year in the UK. If a pandemic strain infected 10 times as many people, it could be expected to cause 10 times as many deaths. It is a numbers game. Much will then depend on the speed with which we can get anti-viral drugs to those affected. One explanation for the virtual absence of deaths outside Mexico so far may be that almost all cases have received rapid treatment with Tamiflu. There will be those who scoff that this is all a figment of my fevered imagination. They will not be satisfied that the WHO's warning of an "imminent" pandemic signals something real until the body bags start arriving in A&E departments. Over the summer months, if cases subside as some scientists expect – flu is harder to transmit in drier, less humid conditions with fewer people congregating indoors – they may scent victory.

That will not be the time to relax. Past experience shows that pandemics can come in waves, each one more virulent than the last. We may have six months to prepare our defences, build up stocks of anti-viral drugs and begin manufacture of a vaccine, before the illness strikes again in the autumn.

We have a pandemic plan, drawn up in the five years since avian flu became a threat in 2003, which sets out the measures to be taken – from distributing anti-viral drugs and establishing telephone helplines to closing schools and banning public events.

Making the vaccine will be the biggest challenge. It first has to be matched to the exact strain of the virus, and then incubated in hens' eggs in the laboratory, a process which may take up to six months. Hundreds of millions of doses would be required which would put immense pressure on the world's laboratories.

Mild flu may evolve into more severe flu over time. Severe flu results in more virus being produced and expelled (in coughing and sneezing) and is thus more likely to be transmitted. As flu viruses are constantly changing, the nastiest strain tends to become dominant, by a process of Darwinian selection.

This is not make-believe – the wolf is real, he's out there, and he's howling at the gate. We don't yet know what damage he can do – but to ignore him would be criminal folly.