Pfizer and Moderna currently have the market on COVID-19 vaccination, but if all goes well, that won’t be true much longer. COVID-19 has existed for barely more than a year, but 64 vaccines are in clinical development and another 173 in preclinical development worldwide, according to the World Health Organization. Dozens of hopefuls are in clinical trials in the U.S. The two inching closest to the finish line here—by Oxford-AstraZeneca and Johnson & Johnson—although behind original schedules, could win emergency use authorization from the U.S. Food and Drug Administration as soon as this spring. Unfortunately, this week Merck announced it has halted development of two potential vaccines for the coronavirus, citing data that showed a lack of immune response.