Citigroup told employees on Thursday that it would require vaccination against Covid-19 as a condition of employment in the United States, making it the first major bank to issue such a mandate. “It has become crystal clear that Covid-19 will not be going away anytime soon,” Sara Wechter, the company’s head of human resources, wrote in a LinkedIn post describing the new policy. Ms. Wechter cited two catalysts for the decision. First, because the bank does business with the federal government, it has an obligation to comply with President Biden’s executive order requiring vaccination for people working on government contracts....