Desperate scenes in the city of Manaus may foretell a dire wave throughout the country. A misguided sense of “herd immunity” has worsened matters, as has the president’s persistent scepticism. We examine history to see how lasers progressed from practical impossibility to utter ubiquity—and the scientific frontiers they are still illuminating. And how clams are protecting lives in Poland. For full access to print, digital and audio editions of The Economist, subscribe here www.economist.com/intelligenceoffer