Covid-19 has disrupted supply chains for the past year and a half. We’ve seen shortages of our favorite things, from ketchup to coffee—but many people hoped that with vaccinations and the world reopening, those woes were behind us. The Delta variant has other plans that could upend the holiday shopping season. Countries at the heart of retail manufacturing, such as Vietnam and Indonesia, are being swept away by surges of the highly transmissible Delta variant of the Covid-19 virus. Popular clothing and shoe brands with factories in these countries, including Nike and Gap, are scrambling to find alternative solutions. These...