It’s part of the ‘usual’ booster Mark but even the manufacturers say that it’s only needed every 3 years. It’s the leptospirosis bit that they recommend annually but in fact it only lasts for 5-7 months and so even boosted dogs aren’t covered for half of the year! :-\
I was involved in clinical trials for Nobivac almost 30 years ago and was told that after the initial puppy vaccinations, my 2 pups titre levels were so high that they would never need boosting again, and that was straight from Glasgow University who were running the trial.
But the next problem is that out of every 5 pups vaccinated, only 3 will take the vaccine because of their maternal immunity and so 2 out of every 5 puppy owners are proudly walking their dogs thinking that they are protected when they’re not! The whole vaccination thing is a minefield, which is why many of us have done our own research and do our own thing. 😉 ;D