News of the study, which will test the response to the vaccine in 30,000 adults who do not have the respiratory illness, pushed shares in Cambridge, Massachusetts-based Moderna up 11% at $81.31 before the bell.
The federal government is supporting Moderna's vaccine project with nearly a billion dollars and has chosen it as one of the first to enter large-scale human trials.
More than 150 vaccine candidates are in various stages of development, with 23 prospects in human trials across the globe. Moderna and British firm AstraZeneca Plc are leading the race with their candidates in late-stage studies.
While rival AstraZeneca said last week it was still on track to be producing doses by September, they and other drugmakers are now targeting delivery of a fully-tested vaccines by the end of the year at the earliest.
"Having a safe and effective vaccine distributed by the end of 2020 is a stretch goal, but it's the right goal for the American people," National Institutes of Health Director Francis Collins said.
Moderna said it remains on track to deliver about 500 million doses a year, and possibly up to 1 billion doses a year, beginning 2021.
The trial is designed to evaluate the safety of Moderna's mRNA-1273 and determine if the vaccine can prevent symptomatic COVID-19 after two doses.
The study also seeks to answer if the vaccine can prevent death caused by COVID-19 and if just one dose can prevent symptomatic COVID-19, among other objectives.