It seems like if the disease is circulating among a population in which they don't often get severely sick (non-vaccinated children), there is still a some, pos

It seems like if the disease is circulating among a population in which they don't often get severely sick (non-vaccinated children), there is still a some, possibly high, chance that it will evolve a mutation that enables infection of the vaccinated adults, if it is allowed to circulate unchecked among children.