I have lost a dog to auto-immune disease that came on a few weeks after his first booster. My other dog vaccinated at the same time had no side effects whatsover.
There are arguments for and against. Many say you cannot make an immune dog more immune by boostering. I read any new vaccine has to kill the old immunity in order to take over. Having nursed an auto immune dog for 7 years, I never vaccinate now. I made my informed choice after reading up extensively on Canine Health Concern, Shirleys Wellness Cafe, and through a UK auto immune support forum.
As far as insurance went, I told the companies my dogs were not boostered, and they still insured them but added the clause they would not pay out for any illness such as lepto, parvo, distemper etc.
And I got a private holiday home to avoid the kennel situation.