Researchers have made good progress toward developing a vaccine to prevent SARS-CoV-2, the new coronavirus that causes COVID-19. Four experimental vaccine candidates have been shown to stimulate both the production of antibodies and T-cell immune responses against the virus in early studies. T-cell immunity is important because it may provide ongoing protection even if antibodies don’t last very long.

Vaccines being developed by Moderna and the National Institutes of Health, the University of Oxford and AstraZeneca, Pfizer and BioNTech, and the Chinese company CanSino are now entering Phase III clinical trials—the last step before approval if they are shown to be safe and effective.

Many experts predict that a vaccine could be ready by the end of 2020 or the beginning of 2021. But this would be faster than any previous vaccine has been developed, and there are currently no successful coronavirus vaccines. Once one or more vaccines are approved, it will still take considerable time before they can be manufactured in large quantities and administered to everyone at risk worldwide.