KEY POINTS
  • The world's biggest Covid-19 vaccine study got underway Monday with the first of 30,000 planned volunteers helping to test shots created by the U.S. government.
  • There's still no guarantee that the experimental vaccine, developed by the National Institutes of Health and Moderna, will really protect.
Medical syringe is seen with Moderna company logo displayed on a screen in the background in this illustration photo taken in Poland.

The world's biggest Covid-19 vaccine study got underway Monday with the first of 30,000 planned volunteers helping to test shots created by the U.S. government — one of several candidates in the final stretch of the global vaccine race.

There's still no guarantee that the experimental vaccine, developed by the National Institutes of Health and Moderna, will really protect.