Canine Lyme and leptospirosis vaccines have the highest rate of side effects. And the need for them tends to be regional, so they aren't included in the core vaccine protocols and they get bumped to non-core and are administered when the risk of the disease outweighs the risk of possible side effects. Almost no vets around here do Lyme, but some do lepto even though it's not a very good vaccine. But incidence of lepto is on the rise, so it's better than nothing.
I had Lyme in 2019 after a trip to our Door County house. Lots of deer in the area. Never saw a tick, but a few days after I got back I got the rash on my neck. My PCP thought I had some kind of heat or allergic rash and was going to send me off to the dermatologist, but I alerted him as to where I had recently traveled. He said he doubted it was Lyme but ordered the blood tests anyway. Came back positive big time (doc was pretty surprised at my immune response) and I went on doxycycline for three weeks. My rash subsided by half after the first dose of the antibiotic. Haven't had any problems since. Glad I didn't get chronic Lyme, which can be nasty.