Focus on the Flu

Since the 1970s, influenza virus used in vaccines has been grown inside chicken eggs. Once the Centers for Disease Control and Prevention predicts next season's target strains, each of the three strains are injected into separate fertilized chicken eggs and  incubated for virus growth. Virus-laden fluids from large batches of eggs are harvested, pooled, and blended into a single vaccine product that includes all three strains. As you can imagine, the process is slow, requiring many months, and, to make the roughly 90 million doses of "trivalent" flu vaccine in a given year, requires lots and lots and lots of eggs—approximately 270 million (90 million doses X 3 eggs per dose).

NIAID-supported researcher William J. Hillegas, Ph.D., of SoloHill Engineering, Inc., a biotechnology firm in Ann Arbor, MI, thinks he's found a better way. He and a group of researchers are investigating whether the use of small beads called microcarriers can lead to a faster, more cost-effective approach for growing virus strains used for influenza vaccines.

With the microcarrier technique, flu virus strains are introduced into the cells of mammals, such as the kidney cells of African green monkeys (Vero cells). The cells are anchored to the beads, which are continually stirred in growth media inside large biological reactors.

The combination of microcarrier beads, Vero cells, and growth media, functioning in a large bioreactor, is considered superior to egg-production technology for a number of reasons:

Flu-infected Vero cells (African green monkey kidney cells), shown in green, grow on microcarrier beads, shown in purple.
CREDIT: SoloHill Engineering, Inc.

• The microcarrier cell culture technology requires much less manufacturing space to produce large quantities of virus
• Microcarriers provide a large surface area on which the Vero cells thrive
• Vero cells growing on beads reproduce rapidly, whereas a hen can only lay so many eggs in a day
• Some of the more dangerous flu strains are toxic to eggs and cannot grow, whereas this would not be the case for Vero cells

Another positive: people allergic to eggs who have been unable to tolerate an egg-produced flu vaccine will likely be able to receive a vaccine made with the microcarrier-bioreactor technology. By speeding up the production process, allowing rapid turnaround when new viruses are discovered, and keeping costs down, the technique could significantly ratchet up our ability to keep ahead of the flu.

For more information please visit SoloHill Engineering's press release on the SoloHill Web site.