Moderna on Friday said the Food and Drug Administration has delayed the approval of its vaccine for respiratory syncytial virus to the end of May due to “administrative constraints” at the agency.

The FDA was expected to make a decision on the RSV shot on Sunday. The agency has not informed Moderna of any issues related to the vaccine’s safety, efficacy or quality that would prevent its approval, the biotech company said in a release.

Investors are watching the upcoming approval closely as Moderna tries to rebound from the rapid decline of its Covid business last year. If cleared, the RSV shot would become the company’s second product to launch in the U.S. after its once-blockbuster Covid vaccine. It would also be the third RSV vaccine to enter the market after shots from Pfizer and GSK rolled out last year.

Moderna said its RSV vaccine is still on track to be reviewed by an advisory panel to the Centers for Disease Control and Prevention during a meeting on June 26 and 27. That panel will vote on recommendations for the shot’s use and intended population, which is necessary before it enters the market.

Moderna has been testing the shot in older adults, who are more vulnerable to severe cases of RSV. The virus kills between 6,000 and 10,000 seniors every year and results in 60,000 to 120,000 hospitalizations, according to CDC data.

“Moderna is very grateful to the FDA for their continued efforts and diligence,” said Dr. Stephen Hoge, president of Moderna, said in a release. “We look forward to helping the agency complete the review of our application, and to the June [advisory] meeting.” 

The approval would demonstrate the versatility of Moderna’s messenger RNA platform beyond treating Covid. The biotech company is using that technology to tackle a range of diseases. Those include RSV, cancer and a highly contagious stomach bug known as norovirus. 

Investors have high hopes for the long-term potential of Moderna’s mRNA product pipeline: Shares of the company are up more than 20% this year after falling nearly 45% in 2023.