Vaccinations

We all want to protect and do the best for our pets, however I personally feel we need to be questioning whether annual vaccinations are really necessary for our pets (we don't get vaccinated every year), and are we actually harming our pets by trying to do the right thing?
Are you aware that no studies have ever determined the optimum frequency of vaccinations?
I think we all would agree kittens and puppies should be given that 1st and 2nd vaccination course, but is vaccination upon vaccination really necessary? 
A few years back I took in a stray puppy, quite quickly the puppy came down with the deadly parvo virus.  I was very upset and also concerned as I had 3 adult dogs between the ages of 6 and 8 years. My dogs had only ever received the initial puppy course vaccinations. I spoke to a vet of my concerns and was told quite calmly that my dogs would be fine, they would not catch it, and they did not catch it, they remained healthy into old age having only ever visited the vet as puppies.
How did the vet know they would not catch it, and why did'nt they catch it? They were not protected, or were they?
I have asked vets why studies have not been carried out to determine whether yearly vaccinations are actually necessary and have been told it is not in the best interest of the pharmaceutical companies to carry out such a study and they are the only ones that could afford to do it.
 
Below are some articles I thought you may find of interest.
 
 
 Pets don't need shots every year
 
Canine Vaccination Concerns - England