The Flu to Come

“For the moment, H1N1 (influenza) is causing the same kind of disease as the regular seasonal flu,” says UC Berkeley School of Public Health professor of epidemiology Dr. Arthur Reingold.  Reingold is a wiry and wry researcher who also advises the World Health Organization on vaccine policy.  We spoke in his living room only hours after he returned from the Cote d’Ivoire.  He also studies AIDS prevention in Africa and Latin America and teaches at UC San Francisco Medical School.

I had asked his opinion on two new studies published in Science on the H1N1 swine flu virus that continued to cause cases and even deaths during the summer.  “True, it’s not the usual flu season in North America, but this is not a usual virus.  It’s new, and there is very little natural immunity to it,” Reingold explained, squinting for effect behind wire-rimmed glasses.  He added there is some evidence of partial immunity among adults older than about 57, presumably who’d been exposed to a similar virus decades ago.

The new studies in Science, one from the US Centers for Disease Control and Prevention, one from the Netherlands, offered details about the molecular structure of the new virus.  In research on ferrets, whose lungs are infected with influenza very much like human lungs, the studies suggest H1N1 may penetrate deeper into lungs and bind more strongly with lung cells than with nose cells “potentially with more severe clinical consequences,” said Dutch researcher Ron Fouchier.  Both studies found the ferrets became sicker with H1N1, and the infections penetrated the gastrointestinal tract.

However, the two studies differed on how infectious the virus may be.  CDC researchers used virus samples from California, Texas and Mexico, where it was first identified, and found the new virus was not as transmissible as ordinary seasonal flu.  The Dutch researchers said their sample, from a patient in Rotterdam, was just as infectious as regular flu.

The new virus, technically called 2009 A(H1N1), may have already mutated in Europe to a slightly more infectious form.  This diabolical evolutionary trick of influenza viruses is called resortment, an ability to recombine genes.  It is why epidemiologists including Reingold are wary of H1N1.  No one knows what it’s going to become.

It is flu season now in the Southern Hemisphere, where cooler temperatures favor the survival of influenza viruses outside the body.  H1N1 resortment is almost certainly going on right now in the bodies of people infected with multiple influenza strains.  This combining genes of various viruses happens randomly, until a particularly strong variant emerges and stabilizes.

“It is worth paying attention to what’s going on in the rest of the world,” says Reingold.  He says whatever virus variant becomes dominant, is the one we’ll have to deal with in the Northern Hemisphere in a few months.

How about a vaccine?  115 million doses of seasonal flu vaccine are normally distributed each year in the US.  A swine flu vaccine would be in addition to that one.  A new swine flu vaccine is now ready for clinical trials, and if all goes well, could be available by November.  But Reingold is cautious.  “It may take two doses per person,” that’s 600 million doses to cover everyone in the United States, he says, and it’s unlikely there will be more than 60 million available.  Some countries, such as Switzerland, likely will have enough for their entire populations.

The good news is not everyone will have to be vaccinated to stop the spread of the virus.  “Herd immunity” is the idea that transmission can be stopped if even a fraction of a population is immunized.  How many people will need to be vaccinated, will depend on how infectious H1N1 becomes.  Even if it is no more infectious than regular seasonal flu, Reingold predicts “we still won’t have nearly enough vaccine this Fall.”

Follow me on Twitter at JohnFowlerTV

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