Scientists at the Food and Drug Administration (FDA) on Tuesday did not take a stance on whether or not to support booster shots of Moderna's (MRNA  ) COVID-19 vaccine, saying data shows two doses are enough to protect against severe disease and death in the United States.

"Some real world effectiveness studies have suggested declining efficacy of Moderna COVID-19 Vaccine over time against symptomatic infection or against the Delta variant, while others have not," FDA scientists wrote in a 45-page document published on the agency's website. "However, overall, data indicates that current U.S.-licensed or authorized COVID-19 vaccine still afford protection against severe COVID-19 disease and death in the United States."

The scientists' report is meant to brief the agency's independent vaccine panel--Vaccines and Related Biological Products Advisory Committee--which is scheduled to meet Thursday to review Moderna's request to authorize COVID vaccine boosters for American adults. The agency could make a final decision within days of the meeting, leaving the U.S. Centers for Disease Control and Prevention (CDC) and its independent advisory committee--Advisory Committee on Immunization Practices--to make the final decision, likely next week.

FDA scientists also failed to take a stance on Pfizer (PFE  )-BioNTech's (BNTX  ) COVID-19 booster shots last month. However, the agency's vaccine advisory panel still recommended third doses of the vaccine for those more vulnerable to severe disease, including the elderly and people with other health conditions; this decision scaled down Pfizer's request for booster shots to be authorized for Americans aged 16 years and older.

Last month, the FDA and the CDC had authorized booster shots of the Pfizer-BioNTech vaccine for more at-risk Americans, including the elderly, adults with underlying medical conditions and those who work or line in high-risk settings such as healthcare and other frontline positions.

Moderna applied for authorization of a third dose with the FDA on September 1. The biotech said its booster shot data is based on a clinical trial of about 170 adults--less than the 318 people who participated in Pfizer-BioNTech's booster shot trial. Moderna found that its booster dose was safe and produced a stronger immune response than seen after the second dose in its late-stage clinical trial.