The world can't wait for a COVID-19 vaccine, but the world might just have to wait a touch longer. According to a report published Thursday on biotech industry news site STAT, citing investigators presumably involved in the research, a phase 3 clinical trial of Moderna's (NASDAQ:MRNA) mRNA-1273 has been delayed. This delay, the length of which was not specified, is due to the fact that Moderna is modifying the protocol of the research.

mRNA-1273 is one of the leading vaccine candidates for COVID-19, and it has vaulted Moderna to the top ranks of coronavirus stocks. Many pundits and infectious disease experts consider mRNA-1273 to be No. 1 among the vaccines currently being developed. The phase 3 trial, involving around 30,000 patients, was to begin this month.

A syringe being filled from a vial.

Image source: Getty Images.

One of the investigators was quoted by STAT as saying that "[m]y understanding was that they wanted to get the first vaccines given in July, and they say they're still committed to do that. As best I can tell, they're close to being on target for that."

Contacted by CNBC for a response, Moderna CEO Stephane Bancel claimed that "we have always said July. And I confirm July." He did not elaborate.

It is not unusual for a company or other entity conducting clinical research to make changes to its protocol. Typically these changes are not drastic, and usually involve a series of adjustments. The STAT article did not provide details about the apparent protocol modifications.

Nevertheless, investors weren't happy with this development. Moderna was down by around 5% in late afternoon trading on Thursday.