I've read for some time that people on Dogpages have vets who only vaccinate every three years. However, until now, my old retired vet, followed by this new practice, still recommended every year because , although it was accepted that certain ones last for three years (indeed when I first had dogs in 1973, the regime was every 18 months to 2 years), lepto needs doing annually and we are an area with high incidence of parvo . The old veet said that, because of the way the vaccines were packaged , ie in two bottles containing a combination, it was not possible to give just the necessary annuals. The present one, who is very up to date on things and is very willing to explain things, says that he has only recently changed because the pharmaceutical company he uses, has now given hits approval, so he was erring on the safe side, incase of repercussions.
He also explained that lepto is not a disease which is passed from dog to dog , like distemper, but is caught on an individual basis from rats. He added that titres can't be used to test all, either (I think he meant lepto), because to test immunity, you have to use live vaccine, so not really a good idea.
My dogs will get an annnual vaccine, but only the full set every three years, from now on.