Looks like SJ and I are crossing replies
He is correct. Frontline is not a 100% sure defense against lyme. What it does do is break the life cycle. Your dog may be the unfortunate last recipient of that tick, but at least the tick will not live to keep spreading the disease. There are other spot-on preventives out there. If what you want is protection from ticks, read the labels. Not all are effective against ticks.
Neither the Fort Dodge nor Merial vaccine has 100% efficacy. Neither can eliminate a current lyme infection. In the case of an existing lyme infection, both are equally as effective in prevent a new lyme infection.
My hope is that by using a three pronged approach that combines being constantly aware of ticks, vaccinating, and using Frontline, that my dog will be safer. Probably me too, since I'm exposed to the same ticks as he.