But the focus on the therapy itself can obscure complicated issues surrounding its delivery. They will be equally decisive in determining whether a vaccine can vanquish this virus.

For example, it is currently unclear how many doses will be needed to fight a disease that will have already expanded into most of the human population. The number of people who have developed natural immunity by the time vaccines arrive will determine whether we need millions or billions of doses. Rapidly producing billions of doses vastly exceeds current vaccine production capacity and would likely require costly repurposing of other facilities, or building even more expensive new manufacturing plants. Yet uncertainty about demand can make it difficult to secure sufficient investment at a fair price per dose…

Even if we get the vaccine we need, we mustn’t fail to get it to the people who need it. We are facing a potential shortage of health care workers to manage mass vaccination efforts, and risk increasing disease transmission by asking people to come for Covid-19 vaccination. If there are not enough doses for everyone, deciding who should get vaccinated within and across countries will need to be prioritized; although this may be a function of whether the vaccine works well enough in particular populations, such as older adults.