Drugmaker Moderna asked the Food and Drug Administration on Thursday to authorize a fourth shot of its Covid-19 vaccine as a booster dose for all adults.

In a news release, the company said its request for approval for all adults was made “to provide flexibility” to the Centers for Disease Control and Prevention and medical providers to determine the “appropriate use” of a second booster dose of the mRNA vaccine, “including for those at higher risk of COVID-19 due to age or comorbidities.”