Even if scientists do develop a safe, broadly effective vaccine, nobody knows how to give it to billions of people. It’ll be scarce at first and – depending on how it works and how it’s made – potentially difficult to transport. They have to figure out how to deploy it now, so that a planet’s worth of people in desperate need will be able to get it.
One approach might be to initially give the vaccine only to members of specific groups. Of course, then someone will have to decide which groups get priority. That order will be hard to figure out. Even if the answer is “whoever is most at risk of dying,” the epidemiological data still isn’t clear on which group meets that criterion.
And “most at risk” isn’t necessarily the right answer. Maybe people at high risk of catching the disease but with a lower risk of bad outcomes should be first in line. That could mean prioritising people with high-exposure jobs that involve a lot of public contact, or that could mean addressing the systemic problems that have led to poorer, African American, and Latinx people facing more illness and death from Covid-19. That’s not easy.