Shares of Moderna Inc. fell 7% on Thursday after medical news site STAT reported a delay in a large trial testing the biotech's potential coronavirus vaccine as the company makes changes to its study plan.

The late-stage trial was expected to start next week, but there is no clarity about how long the delay will last, the report said.

Changes in study plan are common and the company is still aiming to start the trial in July, according to the report.

Moderna reiterated that its trial will begin this month, and that the company has worked with the National Institutes of Health (NIH) for its study plan.

"We expect to be the first to start a Phase 3 trial," the company said in a statement.

Companies including Pfizer and AstraZeneca Plc are racing to develop a vaccine for COVID-19, the illness caused by the new coronavirus that has killed 516,370 worldwide, according to a Reuters tally.

"The furthest along in U.S. testing is an experimental vaccine from NIH's vaccine research center in partnership with Moderna," NIH Director Francis Collins said at Senate Appropriations hearing earlier on Thursday.

"This month we'll seek to enroll 30,000 volunteers with results expected in a few months."

Moderna’s stock (MRNA) was trading at $57.61. The stock has risen more than 200% so far in 2020.