The U.S. Food and Drug Administration on Friday shortened the interval between the primary series of Moderna Inc's COVID-19 vaccine and a booster dose to five months, as it looks to bolster protection against the fast-spreading omicron variant.

The agency expects the shorter interval, reduced by a month for people aged 18 and above, will provide better protection sooner against the variant, which is driving up infections and overwhelming hospitals.

The United States reported 662,000 new COVID-19 cases on Thursday, the fourth highest daily U.S. total ever recorded. The omicron-driven surge in U.S. COVID-19 cases has likely not topped out yet, the Centers for Disease Control and Prevention said on Friday.

The FDA earlier this week cut the interval to get a booster dose of Pfizer and BioNTech COVID-19 vaccine, based on mRNA technology like Moderna's, to five months from six.

"Vaccination is our best defense against COVID-19, including the circulating variants, and shortening the length of time between completion of primary series and a booster dose may help reduce waning immunity," Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said.

People who received Johnson & Johnson's single-dose COVID-19 vaccine can get a booster dose two months later.