Strictly speaking, there is no “settled science” on anything. Old hypotheses are continually giving way to new ones. From Chris Calton at mises.org:
As the “fifteen days to slow the spread” continues to extend indefinitely, the issue of mask mandates has become increasingly contentious. The debate has been exacerbated by the inconsistency of the recommendations of authorities (political, scientific, and imaginary). Early in the pandemic, both the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) advised against the use of masks, except by those who are particularly vulnerable (the elderly and immunocompromised) and their caretakers.
Many of us with some understanding of economics made such arguments at the outset of the debate, not necessarily because of any epidemiological expertise. When you understand the principle of scarcity, policies mandating that healthy teenagers vie for medical products with their more vulnerable grandparents is a formula for exacerbating the most severe outcome of any viral infection. In fairness, many medical experts raised exactly these concerns, even if they did not enjoy the media attention of their more demagogic counterparts.
Regardless of whether or not you agree with the masks-for-all policy, it is heartening to see how well entrepreneurs adapted to the spiked demand, making masks cheaply available in various designs, sizes, and materials, solving the problem of fear-driven people trying to steal masks from emergency rooms. Of course, the dazzling speed of the market response obscures the fact that the adaptation to new conditions and an ostensible emergency would have been even more immediate had private businesses not been forced to wait on Food and Drug Administration (FDA) approval to sell masks to healthcare workers.