This year looks very different from the last when it comes to the pandemic, and that’s largely thanks to the COVID-19 vaccines—three of which, from Pfizer-BioNTech, Moderna and Johnson & Johnson–Janssen, are approved or authorized by the U.S. Food and Drug Administration. The vaccines use different technologies and have reduced rates of severe COVID-19 as well as hospitalizations and deaths. But with new variants, including Delta, that protection, while still strong, is waning. That’s why countries including the U.S. are authorizing booster shots to strengthen that immunity. —Alice Park