You probably want to learn how they make flu, H1N1, or any vaccines. In general, vaccines are made by incubating the virus itself into chicken eggs, then purifying the virus. (see this chart for reference)
As for H1N1, here’s a descriptive process of how the H1N1 vaccine is made:
First, “reverse genetics”, where scientists take the H and the N surface proteins from the H1N1 virus and mix them with a laboratory virus known as PR8.
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