Vaccine effectiveness durations are studied. They vary by the vaccine you’re getting (which I would hope is obvious but your comment is very much a blanket stat

Vaccine effectiveness durations are studied. They vary by the vaccine you’re getting (which I would hope is obvious but your comment is very much a blanket statement). Many of them might decline in efficacy but that can mean 90% effective which is very good. Furthermore many of them have mitigating effects if you do get the diseases anyway that reduce risk of death or complications.