(Adds details from FDA briefing documents)

June 3 (Reuters) - U.S. Food and Drug Administration staff said on Friday Novavax Inc's vaccine reduces the risk of mild-to-severe COVID-19 and that it was likely the shot could provide some level of protection against the Omicron variant.

The FDA analyzed data from Novavax's trial before the Omicron and Delta variant became the dominant strains.

"Based on the efficacy estimate in the clinical trial of this vaccine, it is more likely than not that the vaccine will provide some meaningful level of protection against COVID-19 due to Omicron, in particular against more severe disease," FDA staff said.

In the company's study, which enrolled about 30,000 adults in the United States and Mexico, the vaccine had an efficacy of 90.4%.

The FDA also flagged the possible risk of myocarditis, a type of heart inflammation also associated with rival mRNA vaccines, after the Novavax shot. There were four cases of myocarditis in the trial within 20 days post vaccination.

Staff at the U.S. health regulator published their analysis of Novavax's vaccine data ahead of a meeting of FDA's outside advisers scheduled for next week to discuss the vaccine's authorization in adults.

(Reporting by Manas Mishra in Bengaluru; Editing by Amy Caren Daniel and Saumyadeb Chakrabarty)