The U.S. expansion slowed in August. Factories and service providers reported sharply slower growth, the forecasting firm IHS Markit said in its surveys of purchasing managers. Its index of service-sector activity, the broadest segment of the economy, fell to 55.2 in August, hitting an eight-month low. An index of factory activity dropped to 61.2, a four-month low. A reading above 50 suggests activity—as measured by sales, output, prices and other factors—is growing. But the surveys show that the Delta variant of the Covid-19 virus, which has led to a new wave of infections and hospitalizations and has spooked consumers, is harming the economy. Recent cancellations or postponements of activities in various industries, including concerts and colleges, are likely to hinder consumer spending and economic growth. Country singer Garth Brooks became the latest big-ticket artist to cancel shows. Rice University in Houston moved the first two weeks of the coming semester online, Josh Mitchell and Paul Hannon report.