The generally pose the most danger to those either too young to be vaccinated, or who can't be vaccinated due to legitimate medical concerns. This is not uncomm

The generally pose the most danger to those either too young to be vaccinated, or who can't be vaccinated due to legitimate medical concerns. This is not uncommon, and such children rely on the herd immunity of their peers. Further, as few vaccines are 100% effective, the herd immunity also limits the exposure of viruses to those for whom the vaccine was ineffective.