Merck & Co. Inc. dropped a bombshell Jan. 25, announcing that it was terminating its two COVID-19 vaccine programs, V-590 and V-591, because neither demonstrated convincing levels of efficacy in phase I trials. As a relatively late entrant to the COVID-19 vaccine race, Merck, of Kenilworth, N.J., was never a leading contender in the effort to bring safe and efficacious vaccines to market. Even so, the failure of these programs is a significant setback, given the company’s scale and experience as a global vaccine manufacturer.