Why can't they make more flu vaccine?

Answers to your questions about the news.
Dec. 12 2003 12:51 PM

Why No More Flu Vaccine?

For one thing, there's a shortage of chicken eggs.

The current shortage of flu vaccines has health officials worried about the possibility of a major epidemic. But manufacturers say it will take six months or more to produce additional vaccines. Why does the process take so long?

Because specially purified and fertilized chicken eggs—the kind manufacturers grow the vaccines in—are hard to come by. There are two stages to creating the influenza vaccine each year. First, researchers working with the Food and Drug Administration and the World Health Organization predict which three strains of the flu will hit heaviest in the coming winter. Then, they develop three seed strains—benign versions of each virus for inclusion in the vaccine.


When the seed strains are ready, they need to go forth and multiply. But viruses can't reproduce on their own: They require a host organism, and that's where the eggs come in. The FDA sends the seed strains to manufacturers, who inject them into millions of specially purified fertilized chicken eggs. (Check out this video on the process.) Each egg incubates just one of the three seed strains, which replicate themselves vigorously therein. Then the strains are harvested, tested, and blended together to create the season's influenza vaccine cocktail. All in all, the process can take six months or more.

The hitch is this: In order to get the millions of necessary fertilized eggs laid and delivered on schedule, at exact intervals from February to August of each year, manufacturers must employ considerable logistical savvy. Securing enough eggs can take over a year of advance planning. And once the egg order for a given year is locked in, there's no way to ramp up production. (There's no turning to the grocery store for help, either—the eggs there, though plentiful, are unfertilized.) So, even if a new batch of vaccines were started tomorrow, they probably wouldn't be ready until our flu season is over. In any case, manufacturers are already busy preparing for the flu season in the southern hemisphere.

Flu vaccines have been manufactured this way for decades. But the crisis has amplified calls for overhauling the system. The process of developing seed strains is currently very time-consuming, and some scientists argue they should be developed using "reverse genetics," which eliminates some trial and error. The manufacturing process could also be revamped, possibly by using tissue cultures instead of eggs. Tissue cultures are an industrial-scale version of the petri dish: The seed strains multiply when they're injected into a mammalian cell. (The favored cell for this sort of work, called "Vero," is derived from an African green monkey's kidney.) Tissue cultures are already used to make vaccines for some other diseases, including rabies.

Explainer thanks Dr. Richard Webby of St. Jude's Children's Research Hospital, the Centers for Disease Control Flu Web site, and Aventis-Pasteur's vaccine manufacturing site.

Ed Finn is the director of the Center for Science and the Imagination and an assistant professor in the School of Arts, Media and Engineering and the Department of English at Arizona State University.


Justice Ginsburg’s Crucial Dissent in the Texas Voter ID Case

Even When They Go to College, the Poor Sometimes Stay Poor

Here’s Just How Far a Southern Woman May Have to Drive to Get an Abortion

The Most Ingenious Teaching Device Ever Invented

Marvel’s Civil War Is a Far-Right Paranoid Fantasy

It’s also a mess. Can the movies do better?


Sprawl, Decadence, and Environmental Ruin in Nevada

Space: The Next Generation

An All-Female Mission to Mars

As a NASA guinea pig, I verified that women would be cheaper to launch than men.

Watching Netflix in Bed. Hanging Bananas. Is There Anything These Hooks Can’t Solve?

The Procedural Rule That Could Prevent Gay Marriage From Reaching SCOTUS Again

  News & Politics
Oct. 20 2014 3:53 PM Smash and Grab Will competitive Senate contests in Kansas and South Dakota lead to more late-breaking races in future elections?
Oct. 20 2014 5:39 PM Whole Foods Desperately Wants Customers to Feel Warm and Fuzzy Again
Oct. 20 2014 3:16 PM The Catholic Church Is Changing, and Celibate Gays Are Leading the Way
  Double X
The XX Factor
Oct. 20 2014 1:10 PM Women Are Still Losing Jobs for Getting Pregnant
  Slate Plus
Tv Club
Oct. 20 2014 7:15 AM The Slate Doctor Who Podcast: Episode 9 A spoiler-filled discussion of "Flatline."
Brow Beat
Oct. 20 2014 5:03 PM Marcel the Shell Is Back and as Endearing as Ever
Future Tense
Oct. 20 2014 4:59 PM Canadian Town Cancels Outdoor Halloween Because Polar Bears
  Health & Science
Medical Examiner
Oct. 20 2014 11:46 AM Is Anybody Watching My Do-Gooding? The difference between being a hero and being an altruist.
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.