Preparing For Influenza Season

by Food and Drug Administration (FDA)

(Page 2 of 3)

Preparing for the influenza season each year is a time-critical, highly orchestrated, collaborative effort between the FDA, the CDC, the National Institutes of Health (NIH), the World Health Organization (WHO), vaccine manufacturers, and the health care community.

One of the biggest challenges in the process is to produce a new vaccine every year, says Jesse Goodman, M.D., director of the CBER. "Because the virus mutates, each year's vaccine may be different from the preceding year."

The process begins in late January or early February when an FDA advisory committee meets to recommend which three strains of the virus should be included in the vaccine, based on data from WHO laboratories in more than 80 countries. The FDA makes the final decision on which strains will be included in the vaccine for the U.S. population.

Once the strains are selected, the FDA, CDC, or other WHO collaborating centers can produce reference influenza viruses that are adapted to high growth in eggs. The reference influenza viruses are provided to the licensed vaccine manufacturers to generate the "seed virus" for further manufacturing influenza vaccine.

Manufacturers inject the seed viruses into fertilized chicken eggs, which contain a nutrient in which the virus multiplies.

The manufacturer harvests and purifies the virus from the egg and applies chemical treatments to kill (inactivate) the virus so that it cannot transmit infection. These treatments are done for each of the three strains, which are tested and retested by both the manufacturer and the CBER before being blended into the three-virus strain vaccine.

The CBER produces and provides manufacturers with antiserum, which they use to test vaccine potency for each influenza strain.

Manufacturers ship sample vials of vaccine from each lot, along with their test results, to the CBER for "lot release." The CBER reviews the test results as well as performs its own tests to ensure the accuracy of the manufacturers' tests and the vaccine's safety and effectiveness before releasing each lot for distribution.

Some lots of vaccine may be released as early as July, but manufacturing usually continues until October or later in order to produce and test the large volume of vaccine required for the U.S. population.

It takes about six months to complete influenza vaccine production-from egg to vial-each season. Throughout the process, the FDA discusses technical and manufacturing issues with the companies and inspects each company's facility and manufacturing processes while it is making vaccine.

Why are there vaccine shortages?

Selecting the influenza virus strains each year, preparing the vaccine, and manufacturing and distributing millions of doses all must be precisely timed to make the vaccine available for the influenza season. Any problems encountered during the process may cause delays or shortages. In addition, because the number of companies that make influenza vaccine for the United States is small, a production problem with any company can substantially affect the overall supply.

How much vaccine is available for this influenza season?

Manufacturers have projected making about 100 million doses of influenza vaccine for the 2006-2007 season in the United States, but these projections could change as manufacturing continues. The projected supply is 16 percent more than the 2005-2006 season's 86 million doses and 40 percent more than the 2004-2005 season's 61 million doses. Demand has usually been around 70 million to 75 million doses.

Why doesn't my doctor have influenza vaccine?

Government agencies monitor the vaccine market, but do not control it. Distributing and administering influenza vaccine is mostly a private sector enterprise. The CDC and state and local health departments work to influence distribution through collaborations and recommendations so that vaccine reaches the people most at risk, including older people, health care workers, nursing homes residents, young children, and expectant mothers.

Vaccine distribution is a complex process involving manufacturers, wholesalers, distributors, purchasers, and providers. Some manufacturers sell directly to providers, others work exclusively with wholesalers, and some use both methods of distribution. Since there is no coordinated system that manufacturers and distributors use to deliver vaccines, some health care providers receive their vaccine before others.

Getting vaccinated later still beneficial

Sometimes, vaccine is in short supply early in the season, but there is leftover vaccine at season's end. How much vaccine is produced and distributed plays a role, but so does timing, says Christine Layton, Ph.D., M.P.H., of RTI International, a nonprofit firm in Research Triangle Park, N.C. "The peak demand for flu vaccine is in October and November, when only about 50 percent of the vaccine has been delivered. But it's not until January, generally speaking, that all the vaccine has been available to providers."

And it's usually not until January or later that the influenza disease season peaks in the United States, according to the CDC. The FDA and the CDC support extending vaccination throughout the influenza season, into January and February.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.