Lyme disease can cross the blood brain barrier and cause disease in the brain. This is documented in humans but not yet in dogs, but I believe it can occur in dogs also. That may or may not be the cause of seizures in your dog. Seizures in dogs can occur secondary to trauma, metabolic disease, lesions or tumors in the brain, from a variety of infectious causes, toxins, and, ideopathic causes. Ideopathic means of unknown cause.
Please treat for the Lyme disease, but it probably would also be beneficial to have an MRI or CT scan of your dog's brain to see if there are any lesions there, if you can afford these procedures.
Unfortunately, no vaccine prevents disease 100% of the time. It is estimated that the Lyme vaccine is only 30% to 50% effective.
Additionally, if the seizure was caused by Lyme disease, treating may not eliminate future seizures since the Lyme bug itself may have caused some residual damage to the brain that would be very difficult to eliminate.
Lastly, I am not an veterinary neurologist, so this information is only theoretical on my part. Consulting a veterinary neurologist would be in the very best interest of your dog.