Former college econ major here. Can confirm. At its core, economics is a study of human interactions, with the emphasis on trade. As long as there is decent data, economists could theorize a model for all kinds of things and try to find relationships (or in this case, extrapolate a bit). Of course, since we're still under the narrative that 5 trillion people actually died OF COVID, the "lives saved" projection is going to be a touch high.