People are only vaccinated for viruses as kids. We are then considered immune for life. It is 99.9% likely that it works the same for dogs.
AAHA would not stand behind a protocol if it wasn't safe. A very large number of vets in the US have AAHA accredited offices (meet minimal standards set by AAHA). That is how much vets look to this organization.
You need to do what you're comfortable with though.
I stopped doing titers because I just don't think they are worth it.
UC Davis:
William R. Pritchard Veterinary Medical Teaching Hospital
Colorado State:
CVMBS Minor Template 800 x 600
There are many more like this, just can't find them right now. Some don't post the recommendations on their sites.
I'd hope if there was a change in a vaccine to cover more strains that my vet would let me know about that..
We all need to do what we (and our vets) feel is best. I don't believe vaccinating yearly is in my pup's best interest because there can be side effects from it that we don't see right away. My girl's vet would agree that with all the vaccines out now and how often they are given, we could possibliy be creating a problem.