As the northern hemisphere heads towards its second pandemic winter, some countries have already started to make third doses of vaccine available to their most vulnerable citizens. But scientists disagree about whether offering boosters is the best use of vaccine resources—or necessary at all. And, a big study in Bangladesh finds simple ways to encourage mask use. Also, we reveal our book competition winner. Kenneth Cukier hosts.For full access to The Economist’s print, digital and audio editions subscribe at economist.com/podcastoffer and sign up for our new weekly science newsletter at economist.com/simplyscience.Terms and conditions for the book competition featured in this podcast are available at economist.com/podcast-contest. See acast.com/privacy for privacy and opt-out information.