Guidance from the CDC on who should be prioritized to get the COVID-19 vaccine was meant to be flexible and inclusive. But "the attempt to have equity created more inequity," says one researcher.

With vaccine still scarce, and eligibility differing from place to place, some people have easier access to "extra" doses than others. Careful, ethicists warn. Going out of turn is a slippery slope.

In medical situations, it weighs heavily on doctors and nurses when they are unable to save a life. So, what happens when the decision is not what...