Vaccine strains are grown in nearly 300 million live chicken eggs. The virus is then harvested, inactivated, purified, mixed, and tested before being approved.

How is seasonal flu vaccine made?
  • The entire process, from collecting, injecting and incubating millions of specially produced eggs through the safety tests on the vaccine, takes five to eight months. This means that health officials and providers must decide one year in advance which flu viruses to use in vaccines and how many batches of vaccine to purchase.


  • Even with robotic assistance, “working with eggs is tedious,” says Samuel L. Katz, M.D. of the Duke University School of Medicine, and a former member of the vaccine advisory committee for the U.S. Food and Drug Administration.


  • Because of the nature of flu vaccine production, vaccine companies must place their egg orders 5-8 months in advance before they begin producing vaccines.


  • This process consumes hundreds of millions of eggs (270 million or more for the United States alone) to produce a sufficient supply of vaccine for the United States.

  • “The egg method isn't very flexible if you need to rapidly ramp up vaccine supply,” said Jonathan Seals, Ph.D., Acting Director of the Strategic Science and Technology Division with the Biomedical Advanced Research and Development Authority (BARDA) at the U.S. Department of Health and Human Services. “Vaccine manufacturers need to arrange for egg supplies months in advance - and you can't tell a chicken to lay more eggs.”
  •  Modern cell culture-based production methods are now being researched, but are years away from completion. Today, influenza vaccines are prepared in a modernized version of original methods.