May 31 (Reuters) - The U.S. Food and Drug Administration has approved Moderna's next-generation COVID-19 vaccine for everyone aged 65 and above, the company said on Saturday, the first endorsement since the regulator tightened requirements.

The vaccine has also been approved for people aged 12 to 64 with at least one or more underlying risk factors, Moderna said in a statement.

The Department of Health and Human Services, under the leadership of long-time vaccine skeptic Robert F. Kennedy Jr., is increasing regulatory scrutiny on vaccines.

The FDA said on May 20 it planned to require drugmakers to test their COVID booster shots against an inert placebo in healthy adults under 65 for approval, effectively limiting them to older adults and those at risk of developing severe illness.

The Moderna vaccine, branded mNEXSPIKE, can be stored in refrigerators rather than freezers, to offer longer shelf life and make distribution easier, especially in developing countries where supply-chain issues could hamper vaccination drives.

The Centers for Disease Control and Prevention, which Kennedy also oversees, said on Thursday that COVID vaccines remain an option for healthy children when parents and doctors agree that it is needed, stopping short of Kennedy's announcement days earlier that the agency would remove the shots from its immunization schedule.