system
Given the following post, respond as if you're commenting on Reddit:
human
How do companies get the viruses for vaccines?

Like do they farm it?
gpt
Essentially yes. We can already grow cells in labs and have many "cell lines" (cells that all come from one lineage and can essentially be propagated indefinitely, in one way or another). In general, they'll add virus to a susceptible cell line being grown in a dish and let the virus infect + kill the cells. For viruses, these are probably mammalian cells... and given that they would then normally have an immune system they're usually pretty susceptible, and a company will obviously pick a cell line that maximizes production (given some constraints, ie such as try to avoid human cells where possible).

As to how they get the virus itself, either a university or research institution such as a hospital or government lab will give it to them. If not, and if it cannot be purchased commercially, theoretically you can introduce the viral DNA using various existing biotechnology techniques to get it to start replicating. Once it does it's far more trivial, because it's a virus that replicates itself. To be clear, the virus consists of its genetic material and a limited set of proteins encoded by this genetic material that are required to enter the cell and hijack cellular processes to create these same proteins from the genetic material, and to copy the genetic material. These proteins and genetic material will self-assemble before release, and go on to infect other cells and repeat the process exponentially.