for example, in a test case scientists have gone from flu sequence to midscale production (i.e. enough for first responders) of flu vaccine within something like 4 days. The backstory is great - the lead researcher arranged for FedEx to pick up the finished DNA sequences at his home at midnight (I don't remember why it couldn't be picked up at the lab but there was a reason) and he was worried that his neighbors would think that he was a drug dealer.. This means one could go to large scale production (enough for a population) within weeks to months.

Unlike the seasonal flu shot, this vaccine is tailored to the emergent strain.