I have Medicare AAdvantage which seamlessly covers Parts B and D, so that particular thing doesn't happen. However, until this year Medicare did not cover the shingles vaccines AT ALL, no matter what kind of coverage you had. That totally sucked and made no sense at all, since the vaccine is particularly important for people over 65. And it was really expensive - almost $400 for the two-shot regimen. I think that has finally been remedied starting in 2023.

Incidentally, newer studies have debunked the old belief that you need a tetanus shot every 8-10 years. Not sure about pertussis or diptheria.

https://news.ohsu.edu/2016/03/22/study-shows-tetanus-shots-needed-every-30-years-not-every-10