Now, a year after the pandemic first erupted, three COVID vaccines have been given emergency authorization by either the U.S. or U.K., as well as other countries. But impressive as they are, these vaccines alone will likely not be sufficient to end the pandemic, experts say. Luckily, there are hundreds of other COVID vaccines under development—including many with new mechanisms of action—that could prove to be effective and cheaper and easier to distribute. And mRNA vaccines such as Pfizer’s and Moderna’s—touted by many as the future of vaccinology—have never previously been brought to market. But instead of injecting the entire spike protein, they have homed in on the virus’s “Achilles’ heel”: the receptor binding domain (RBD), the portion of the spike protein that directly fuses with human cells.