U.S. stocks closed lower on Wednesday, with the Dow Jones Industrial Average falling nearly 700 points, a drop of over 1%. Walmart's stock fell 9% after the company reported its smallest sales growth in over six years, reflecting cautious spending by some U.S. consumers. Moderna's stock dropped 24%, a day after it had surged 177%, marking the S&P 500's largest single-day gain in 25 years. The S&P 500 fell 0.9%, and the Nasdaq index dropped 1%.