In the post-9/11 world, the phrase “national security” conjures up images of dirty bombs, jihadists, white powder and biohazard labels. It should also bring to mind another picture: an egg.

As we enter flu season, scientists and public health officials are ramping up efforts to combat the expected rise in cases of H1N1 flu. Hospitals, doctors’ offices and clinics started receiving the vaccine earlier this month, but so far it’s only available in limited quantities and will have to be allocated piecemeal across the country. And some experts predict that the H1N1 epidemic will peak before the majority of vaccine doses can be produced.

The most common method of making flu vaccines requires chicken eggs to incubate viral strains. It takes three eggs to produce a single dose of H1N1 flu vaccine. Vaccination of every American would require more than 920 million eggs.

If that sounds like a big number to you, try asking a chicken farmer. Thankfully, America’s modern agriculture system makes production on that scale possible. For now.

If the latest fad of animal-rights activism continues, however, our capacity to produce eggs — and vaccines — may be threatened.

Last fall, Californians voted to approve a ballot initiative advertised as promoting animal welfare. One of the things that law actually did, however, is require that egg-laying hens be raised without cages.

Proposition 2, as the measure was called, received major support from the so-called Humane Society of the United States, a “humane society” in name only. (HSUS essentially functions as a richer and more policy-oriented sister to the better-known wing nuts at People for the Ethical Treatment of Animals.) Groups like PETA and HSUS are driven by an animal-“rights” agenda that seeks the end of animal agriculture as we know it.

What do animal rights activists have to do with the flu? Lobbying by these groups has the potential to diminish our domestic “egg security” by driving egg farmers out of business — or at least out of the United States.

Complying with Proposition 2 is already proving prohibitively costly for Californian egg producers. And businesses are learning that this alleged “progress” for animal welfare has opened a Pandora’s box of activist-driven problems. Last month, one California producer announced the construction of a new, $3 million, Proposition-2-“approved” henhouse. HSUS immediately attacked it in the press over how much room was enough for wing-flapping.

It could take years in the courts and millions in legal costs for the company to learn if it has to build yet another henhouse. Chances are it won’t stick around long enough to find out.

Ultimately, the animal-rights industry won’t be satisfied with just a “cage-free” law. One HSUS director told his organization’s Taking Action for Animals conference in July that “if anyone says ‘cage-free’ is 100 percent humane, 100 percent cruelty-free, just know that that’s not accurate.”

HSUS is happy to make livestock farming a thing of the past because its core philosophy is veganism: no meat, no eggs, no dairy. In July, that same HSUS spokesman spoke of an immediate need to “reduce the number of animals raised for food” in the United States.

According to a 2008 University of California economic analysis, a nationwide switch to cage-free eggs would cost consumers 25 percent more for their omelets. With HSUS winning concessions from Michigan farmers and openly targeting Ohio next, that scenario isn’t a mere figment of anyone’s imagination.

But there’s an even bigger picture: Once egg farmers tire of being hassled by chicken advocates, they can (and will) simply move abroad, mostly to Mexico, taking jobs (and eggs) with them. And as more U.S. producers relocate south of the border, our response to a future pandemic could hinge on the quality — and affordability — of a billion hastily imported huevos.

It’s clearly reckless to allow our national food policies to be written by animal activists who see chickens (and their eggs) as legal persons. Giving those same radicals the power to put public health at risk makes even less sense.

PETA founder Ingrid Newkirk famously said that “even if animal tests produced a cure for AIDS, we’d be against it.”

Does that sound like someone you’d like to see connected to our supply of flu vaccine?

Me neither.