US regulators on Tuesday posted a largely positive review of Moderna Inc’s SARS-CoV-2 vaccine, signaling that the nation might soon have a second shot available to prevent COVID-19.

The staff of the US Food and Drug Administration (FDA) released its briefing document ahead of Thursday’s advisory committee meeting on Moderna’s mRNA-1273 vaccine. The product is similar to the first COVID-19 vaccine cleared for use in the United States. Both the Moderna and rival Pfizer-BioNTech vaccines use a new approach — mRNA instructions — to spur the immune system into action.

The FDA on December 11 granted an emergency use authorization (EUA) for the Pfizer-BioNTech COVID-19 vaccine for people ages 16 and older, following a vote in its favor by an advisory committee. Both the Pfizer and Moderna vaccines are intended to be taken in a two-dose regimen.

Cambridge, Massachusetts-based Moderna is seeking an EUA for use of its vaccine in people ages 18 and older. In the briefing document, the FDA staff noted that study data indicates the primary efficacy endpoint demonstrated vaccine efficacy (VE) of 94.1% (95% CI, 89.3% – 96.8%), with 11 COVID-19 cases in the vaccine group and 185 COVID-19 cases in the placebo group.

The FDA staff review also notes that the data gathered so far suggests the Moderna vaccine works better in younger people and may protect against severe forms of COVID-19.

“The VE in this analysis when stratified by age group was 95.6% (95% CI, 90.6% – 97.9%) for participants 18 to younger than 65 years of age and 86.4% (95% CI, 61.4% – 95.5%) for participants 65 years of age and older,” the FDA staff said in the review. “A final secondary efficacy analysis also supported efficacy against protocol-defined severe COVID-19, with 30 cases in the placebo group vs 0 cases in the vaccine group.”

The FDA staff also said data from a November 11 interim analysis of about 30,350 study participants “supported a favorable safety profile, with no specific safety concerns identified that would preclude issuance of an EUA.”

Bell Palsy Cases

There have been cases of Bell palsy seen in testing of both the Pfizer-BioNTech and Moderna vaccines, but neither product has been definitively linked to this risk. The handout prepared for clinicians for the Pfizer-BioNTech vaccine mentions that there were four cases of Bell palsy in people who received the active drug in testing, but none reported in the placebo group.

“Currently available information is insufficient to determine a causal relationship” with the Pfizer-BioNTech vaccine, the clinician handout says. “There were no other notable patterns or numerical imbalances between treatment groups for specific categories of non-serious adverse events (including other neurologic or neuroinflammatory, and thrombotic events) that would suggest a causal relationship to Pfizer-BioNTech COVID-19 vaccine.”

As with the FDA briefing for the advisory committee meeting on the Pfizer-BioNTech vaccine, the agency staff made note of cases of Bell palsy seen during testing of the Moderna vaccine in the document posted Tuesday.

In the review of the Moderna vaccine, the FDA staff noted “a small imbalance in the number of participants reporting Bell’s palsy (facial paralysis), with 3 vaccine recipients and 1 placebo recipient reporting this medically attended adverse event.”