A U.S. company says it’s on track to begin a huge study next month to prove if its COVID-19 vaccine candidate really works. Moderna Inc. is developing the experimental shot with the National Institutes of Health. It’s still wrapping up necessary earlier stage testing. Moderna said Thursday it planned next month to test the vaccine in 30,000 volunteers, some given the real shot and some a dummy shot. About a dozen candidates are in early stages of human testing in the global race for a vaccine. And governments are stockpiling millions of doses in hopes that some pan out.