I'm attaching an image of a table documenting duration of immunity for various types of vaccine from a paper co-authored by Dr. Schultz in 2001. You really have to go by the challenge study results--that's where they try to infect the vaccinated dog with the disease. Those types of studies are the most accurate. The paper itself may be behind a paywall, but in case it's not, here is the link:
http://www.vetsmall.theclinics.com/a...%2950603-8/pdf
The table also indicates whether or not the titer test correlates with immunity for the various types of vaccinations. At the time this paper was released, there were no challenge studies available for the rabies vaccine. Schultz's current research (linked in a previous post) shows that rabies vaccine is good for at least five years, and the study is still ongoing.
Not all titer tests are correlated with immunity based on challenge studies, so you have to be really careful in interpreting titer test results.
(Somehow, we've drifted way off topic from dog flu, but that's okay.)