Moderna’s investigational vaccine for the novel coronavirus has been cleared by the US Food and Drug Administration to proceed to phase two of a study, the company said Thursday in a press release.

The next phase of the trial is expected to begin shortly, it said.

The vaccine, mRNA-1273, was the first US vaccine to start clinical trials in the United States. Moderna said it is finalizing protocol for a phase 3 study which is expected to begin in early summer.