Shares of Johnson & Johnson /zigman2/quotes/201724570/composite JNJ -0.46% gained 5% in premarket trading on Monday after the company said it had identified a lead candidate in its efforts to develop a COVID-19 vaccine. J&J said Monday it plans to begin Phase 1 clinical trials of the vaccine candidate in humans in September, and the investigational vaccine may be ready for emergency use authorization from the Food and Drug Administration by early 2021. The company is also scaling up its vaccine manufacturing capabilities in the U.S. and abroad as part of its commitment to bring "an affordable vaccine to the public on a not-for-profit basis for emergency pandemic use." A number of companies including Moderna Inc. /zigman2/quotes/205619834/composite MRNA -0.72% are developing vaccines that would prevent infections from the novel coronavirus that has sickened more than half a million people worldwide. Year-to-date, J&J's stock is down 15%, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.11% has tumbled 21%.