As the highly transmissible delta variant surges through the United States, breakthrough COVID-19 cases — infections among fully vaccinated people — have become more common, scientists say. In this NPR article, science writers Selena Simmons-Duffin and Rob Stein share what we know — and don’t know — about breakthrough cases, including whether fully vaccinated people who get sick can spread the virus (they can); whether they can develop long-haul COVID-19 (it’s possible); and whether they can be hospitalized and die (it’s rare). “Severe cases among vaccinated people are possible but extremely rare — the vaccines dramatically reduce the risk of serious illness that leads to hospitalization or death. And 97% of those currently hospitalized with COVID-19 are unvaccinated,” the authors write.