Lessons from the swine flu pandemic

What has the swine flu pandemic taught us, asks Wendy Orent, writing for the Los Angeles Times.

We have learned a lot from the 2009 H1N1 swine flu outbreak.

We have learned, for example, that one basic assumption about pandemics was wrong.

You don't need a radical mutation in a flu virus to produce a pandemic.

All you need is enough change within a surface protein for a new strain to blow past acquired immunity and blaze around the world, as this one did.

And we've seen that not every pandemic strain is especially lethal.

The centres for disease control and prevention in Atlanta estimated 11,690 Americans had died of swine flu by mid-January.

In a "normal" flu season, it estimated 36,000 Americans died.

As Peter Palese, an eminent flu virologist from Mount Sinai Hospital in New York, put it, "We were lucky - this was a mellow virus."

It lacked the virulence factors that make highly pathogenic bird flu, or the 1918 pandemic flu virus, so deadly.

In the beginning, the pandemic seemed to have an ominous affinity for the young.

But this turned out to be mostly a matter of resistance.

Many people born before 1957 had some immunity to the virus because of their exposure to a previous H1 outbreak.

So older people, the usual victims of seasonal flu, caught the new virus at much lower rates.

And even among young people, though the attack rate was ferocious and many millions were infected, only a tiny percentage of those who got the flu died.

Another thing we've learned is that a safe, effective new flu vaccine can be produced fairly rapidly.

In 1976, when 40 million people were quickly immunised against a pandemic that never came, several hundred of those receiving inoculations fell ill with Guillain-Barre paralysis, leaving Americans sceptical about fast-turnaround vaccines.

This year was different.

"We've had intensive safety monitoring because of the experience with 1976," said Anne Schuchat, director of the National Centre for Immunisation and Respiratory Diseases, adding that "the safety record looks fantastic".

On the other hand, we have learned more about the virulence of the anti-vaccine lobby, which persuaded far too many people not to get vaccinations or - even worse - not to vaccinate their children.

Dr Paul Offit, chief of infectious disease at Children's Hospital of Philadelphia, worries the anti-vaccine fringe has gained the upper hand and is calling the shots on some important matters of public policy.

For example, he notes, no-one in America dared put adjuvants - immune-stimulating chemicals - into the vaccine, a move that would have stretched the limited supply.

Both Canada and Europe used the chemicals with no ill effects.

In Europe, vaccine makers used squalene, which meant children needed only one shot instead of two.

But say the word "squalene" and multitudes of Americans shudder: squalene in anthrax shots has been fingered by some anti-vaccine activists as the cause of Gulf War Syndrome.

That squalene is a chemical precursor to cholesterol, and made in the body every day, means nothing to them.

Though H1N1 transmission appears to be dying down, we surely haven't seen the last of this virus.

Some experts fear the virus could evolve around existing immunity.

Perhaps the most important lesson we can learn from this pandemic is where it came from and how we can prevent another one.

Columbia University virologist Raul Rabadan, who has studied rates of mutational change in swine, bird and human flu, says the pandemic virus most likely emerged from a pig herd.

Circumstantial evidence points to a giant, high-density pig farm in the small (3000 people) town of La Gloria, in Veracruz, Mexico, where, according to an Associated Press report, about 450 people were diagnosed in late March with acute respiratory infections.

There, too, the pandemic's "index case", a 5-year-old who first tested positive for H1N1, was identified.

Gregory Gray, a University of Florida influenza researcher, has shown in several studies that 12-21% of Iowa pig farmers have antibodies to H1 pig influenza viruses.

His team's studies suggest workers may pass these on to their families.

But generally the pig viruses stop there.

This one didn't.

No-one knows why.

Wendy Orent is the author of Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease.