
You will receive conflicting advice on this as people will tend to go off their experience and here is mine:
Annual boosters are not necessary, most vaccine manufacturers advice every 3 years for boosters - there is an argument that the lepto needs to be done yearly, although I was advised this vaccine only lasts between 3-9 months so the dog is unprotected for much of the time anyway and, the strains used in the vaccine are not the strains found in the uk. It is also the vaccine that most dogs react badly to.
I was also advised by a a specialist on the subject of vaccines that once a dog is immune then that immunity will last for 7 years to life, and therefore once dogs have had their puppy vaccines a titre test (blood test) yearly is all that is necessary to establish if they still have immunity. This is what they take to find out if the rabies vaccine has worked, so you need to ask your vet for this - who will probably try to talk you out of it.
My last dog died aged 3 from an adverse reaction to his booster :( and now, my dogs are vaccinated as a puppy and then not again, they have had titre tests and once when one of their titres was low for parvo I was unable to find a vet in the area who would do the single parvo vaccine, all wanted to give the whole lot - so I went down the homeopathic route of nosodes and when they need to go into kennels the homeopathic vet signs their vaccine card advising they are protected.
It's a difficult one because we all want to keep our dogs as safe as we possibly can, but after the horrific experience I had with Spangler, I am now extra careful with vaccines and any drugs used on my boys (aged 4 & 5) and I'm pleased to say they are very healthy :)