Why Making a Covid Vaccine Is Only the First Hurdle

In the quest to develop vaccines against Covid-19, researchers are on the cusp of overcoming challenges that typically require years if not decades to beat. After the first experimental shots produced positive results in late-stage trials — a huge feat in itself — drug companies and health officials will face another set of obstacles in inoculating hundreds of millions of people around the world. Assuming developers gain approval soon, a rollout could start by the end of the year. Still, a num