The Oxford/AstraZeneca vaccine has advantages that make it an attractive possibility. It can be stored at normal refrigeration temperatures, and its price is low relative to its competitors. Public health experts have long targeted it as ideal for use in lower and moderate-income countries because of these features.

The problem is that its U.S. Phase III trial was delayed because of an adverse event investigation in the fall, and the data from the international trials used by the U.K. government are difficult to interpret due to unplanned modifications to dosing levels.