Pigs will fly before we take flu seriously

Even if H1N1 remains benign for a while, it could easily come back in more virulent form
May 4, 2009
Mark Henderson

It started out as a blend of two swine viruses. It has some genes that originated in bird flu. And as far as many pundits are concerned, the pathogen officially known as influenza A (H1N1) would be better named flying pig disease.

As swine flu began to spread around the world last week, prompting the World Health Organisation to declare that a pandemic looks imminent, a second virus has followed inexorably in its wake. Its symptoms are angry claims that the threat is illusory and overhyped, and it has infected plenty of people who ought to know better.

Swine flu, they hold, poses none of the hazards that have been claimed for it. It has so far caused only 20 confirmed deaths, all but one of them in Mexico. It responds to antiviral treatment. Scientific analysis has suggested it is a mild strain. Yet it has prompted warnings that 40 per cent of the population could become infected, causing millions of deaths.

For some media commentators H1N1 is just another scare, an unfounded panic like those that blew up over the MMR vaccine and avian flu. It may help editors to shift newspapers, scientists to win grants, public health officials to justify their existence and pharmaceutical companies to sell antivirals, but they are doing so by “manipulating fright”.

Most health scares are indeed groundless, and some, such as MMR, have caused grave damage to public health. Swine flu, however, is not one of them. It is a threat that must be taken extremely seriously, even if the death toll does not rise sharply in the next few weeks.

While scientists are describing swine flu as a mild strain, this terminology is relative. There is no such thing as mild flu - it is always a serious infection that can be life-threatening. The danger from this particular virus is especially acute because it is new: our immune systems are naive to it, and this raises the likelihood that it will infect a very large number of people.

Swine flu could thus have severe effects even if it is not particularly lethal. Virologists are likening it to the strain that caused the 1968-69 pandemic, which was also considered mild: it killed about one in 1,000 of those it infected. Its novelty, however, meant that it infected more than a billion people worldwide, causing a million deaths. A virus with a similar virulence and attack rate would infect about 18 million people in Britain, and kill 18,000, three times as many as usually die from seasonal flu. The NHS would be stretched to its limits, so deaths from other causes would rise as well. The pandemic would be mild only by degree.

There is also no guarantee that this virus will continue to be comparatively benign. It is a fact of life that flu mutates fast, and there is every possibility that H1N1 will become more virulent, or resistant to antiviral drugs. The 1918-19 Spanish flu began as a mild virus in the northern hemisphere spring. It returned with a vengeance in the winter, bearing a mutation that enabled it to kill 50 million. If swine flu disappears over the summer, we can expect it back when the weather gets colder and wetter. It might well have turned nastier by then.

The mutability of influenza also guarantees that even if this strain does not cause a severe pandemic, another will emerge to trigger one before long. Past flu pandemics have been roughly cyclical, occurring at intervals of 10 to 40 years, and the last one was more than four decades ago. It is possible that swine flu will not turn out to be very serious. We would then have dodged a bullet, but the gun that fired it would still be loaded and pointing our way.

If we are unlucky, the next one could be bird flu. The H5N1 virus has largely disappeared from the headlines; indeed, it is often cited as a prime example of a health threat that never materialised. But it hasn't gone away. New cases have been reported recently in Indonesia and Egypt, and 60 per cent of the 421 people confirmed as infected to date have died. Should this exceptionally virulent virus mutate to spread easily from person to person, the implications would be dire. The swine flu outbreak makes this no less likely. It could even increase the risk, as the two strains could “reassort” into a new virus.

Whatever shape the looming swine flu pandemic takes, we cannot afford complacency. In many ways, this will be particularly true if its effects are mild. Public health measures such as isolation, antiviral treatment and “social distancing” may yet limit its impact, but if such efforts are successful they will themselves feed a backlash. Critics will carp at the dog that didn't bark, while forgetting it was muzzled.

While a swine flu pandemic remains the greatest danger, a threat that passes will carry grave risks of its own. If it promotes misguided suspicion that surveillance, public health plans and antiviral stockpiles are a waste of time and money, it will leave us ill-prepared the next time around. And there will be a next time: pigs will fly before influenza stops mutating. Our pandemic defences should not stop at flu: we also need to guard against flu fatigue. It can be almost as hazardous as the virus itself.