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.

Advertisement

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.

TODAY IN SLATE

Politics

The Democrats’ War at Home

How can the president’s party defend itself from the president’s foreign policy blunders?

Congress’ Public Shaming of the Secret Service Was Political Grandstanding at Its Best

Michigan’s Tradition of Football “Toughness” Needs to Go—Starting With Coach Hoke

A Plentiful, Renewable Resource That America Keeps Overlooking

Animal manure.

Windows 8 Was So Bad That Microsoft Will Skip Straight to Windows 10

Politics

Cringing. Ducking. Mumbling.

How GOP candidates react whenever someone brings up reproductive rights or gay marriage.

Building a Better Workplace

You Deserve a Pre-cation

The smartest job perk you’ve never heard of.

Hasbro Is Cracking Down on Scrabble Players Who Turn Its Official Word List Into Popular Apps

Florida State’s New President Is Underqualified and Mistrusted. He Just Might Save the University.

  News & Politics
Politics
Sept. 30 2014 9:33 PM Political Theater With a Purpose Darrell Issa’s public shaming of the head of the Secret Service was congressional grandstanding at its best.
  Business
Moneybox
Sept. 30 2014 7:02 PM At Long Last, eBay Sets PayPal Free
  Life
Gaming
Sept. 30 2014 7:35 PM Who Owns Scrabble’s Word List? Hasbro says the list of playable words belongs to the company. Players beg to differ.
  Double X
The XX Factor
Sept. 30 2014 12:34 PM Parents, Get Your Teenage Daughters the IUD
  Slate Plus
Behind the Scenes
Sept. 30 2014 3:21 PM Meet Jordan Weissmann Five questions with Slate’s senior business and economics correspondent.
  Arts
Brow Beat
Sept. 30 2014 8:54 PM Bette Davis Talks Gender Roles in a Delightful, Animated Interview From 1963
  Technology
Future Tense
Sept. 30 2014 7:00 PM There’s Going to Be a Live-Action Tetris Movie for Some Reason
  Health & Science
Medical Examiner
Sept. 30 2014 11:51 PM Should You Freeze Your Eggs? An egg freezing party is not a great place to find answers to this or other questions.
  Sports
Sports Nut
Sept. 30 2014 5:54 PM Goodbye, Tough Guy It’s time for Michigan to fire its toughness-obsessed coach, Brady Hoke.