The overlooked superpower of mRNA vaccines

Individuals facing the threat of COVID-19 may care most about a vaccine’s ability to forestall grave disease that could lead to a hospital bed or worse. And a number of vaccines perform that vital task well, including those from Johnson & Johnson and AstraZeneca, which are based on genetically engineered cold viruses, as well as the not-yet-authorized protein vaccine from Novavax. But for public health experts trying to halt a global pandemic, shutting down even the mildest infections is also crucial, especially as the highly infectious Delta variant surges in scores of countries.