I work a lot with secondary datasets and I’m always looking for new and interesting resources. There is a CDC site that tracks flu reports and with a bit of effort, you can get the raw data behind these reports. A blogger, hrbrmstr (Bob Rudis, if you dig long enough to find his real name), developed an R package that makes it easy to import this data into R. He illustrates the use of this package with a graph that shows some interesting trend lines across several major cities.
Bob Rudis, New R Package: cdcfluview — Retrieve Flu Data from CDC’s FluView Portal. Blog post on rud.is and reposted at R-bloggers, 2015-01-10. Available in html format.