John M. Barry, who literally wrote the book on the Spanish Influenza Pandemic, has an article on the Swine Flue outbreak that is a must read.

I also need to read his book.

I had not previously realized that the initial Spring outbreak was very mild, and it was the Autumn outbreak that had the virulence that we now remember the disease for.

Money quote is at the end:

In all four instances [Influenza Pandemics], the gap between the time the virus was first recognized and a second, more dangerous wave swelled was about six months. It will take a minimum of four months to produce vaccine in any volume, possibly longer, and much longer than that to produce enough vaccine to protect most Americans. The race has begun.

Go read.