As countries like the United States and United Kingdom inoculate their residents with never-before used vaccine technology, others, including Russia, China, and India, are investing in more traditional approaches, like inactivated coronavirus vaccines. But no matter the technique, together they have the potential to create multiple lines of defense against SARS-CoV-2. Science senior correspondent Jon Cohen explains how each of these vaccines can protect us from severe illness—and what understanding the details of our immune responses could mean for the future of human trials.