LONDON — A coronavirus vaccine is coming soon. The question now for the world is who will be at the front of the line for an injection.

In the initial months, vaccines will certainly be rationed. Demand will outstrip supply. There will be millions of doses available, not billions.

Health ministries around the globe are just now beginning to create the lists that will prioritize vaccine allocation within their countries. It is harder than it might seem.

Nations need to wrestle with questions of fairness and expediency. They need to determine how to balance saving the lives of the most vulnerable against stopping the spread of the virus against the need to keep essential workers — however they are defined — on the job.

Tough decisions await: Who goes first, second or third?