by Jacob Jenkins

Created on: May 12, 2009   Last Updated: May 14, 2009

To say that the production of a influenza vaccine is a straightforward process requires ignoring the difficult work that goes into selecting virus strains for production and creating new production techniques. Selecting the strains and designing the processes that create a successful vaccine is an arduous process that involves analysis, creativity, and intense debate by some of the most intelligent members of the infectious disease community.

Though the industry is on the verge of sweeping changes, vaccine production still primarily is accomplished via a process that dates back to the 1940's. This involved injecting a single strain of a virus into a fertilized egg and allowing it to reproduce. The first stage of this process can take 3-5 weeks in order to produce enough seed to inoculate enough eggs for mass production. Then it takes another 4-6 months, depending on the amount needed, to produce enough for a large population.

The next step for turning the newly grown microbes into a vaccine depends upon what type of vaccine they will be used in. The first type are called live attenuated vaccines; these vaccines consist of viruses that are still alive, but are weakened to the point where they can barely reproduce. This type is mostly used to create viral vaccines, whereas the next type of vaccine, the inactive vaccine, is used primarily for bacterial vaccines. The inactive vaccine is created by chemically killing the virus, often by using formaldehyde. Although the virus is no longer alive the body's B cells still attempt to attack the virus's proteins and form antibodies. Lastly, in addition to the vaccine, chemical stabilizers are added to ensure the solution's potency.

For seasonal influenza viruses, both types of vaccines are made. The inactive vaccine is injected and the live type is given in the form of a nasal spray. According to John Bradley, M.D., the live-attenuated (intranasal) influenza vaccine is better at protecting against the flu virus because, by being an active virus, it provides broader protection by mimicking a natural infection better than an inactive vaccine.

Despite the egg-based process being very effective, it still has many drawbacks. The first is the time required to produce a large quantity of vaccine (4-6 months) and the millions of chicken eggs required, around 900 million for 300 million doses of vaccine. Another drawback is that some viruses, particularly those with the H1 protein, don't grow very well in chicken eggs. The H1N1

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