According to persons familiar with the situation, the US Food and Drug Administration is leaning toward authorizing half-dose booster doses of the Moderna Inc. coronavirus vaccine, satisfied that it is efficient in bolstering protection.

Following the approval of the Pfizer Inc.-BioNTech SE injection, the authorization would pave the way for a more extensive booster campaign in the United States. In the United States, about 170 million completely vaccinated persons received the Moderna or Pfizer doses, accounting for 92 percent of the total inoculated to date.

Before a possible announcement, the persons spoke on the condition of anonymity. It is unknown when the information will be made.

Moderna's initial inoculations included 100-microgram dosages, and the company's petition to authorities amounted to a request for permission to make a half-dose booster, allowing Moderna to produce more. Different dose levels for boosters would be introduced as part of any authorization. For instance, Pfizer's shot has a 30-microgram initial dosage and a 30-microgram booster.

On Tuesday night, Moderna declined to comment. The White House and the Food and Drug Administration both declined to comment.

According to President Joe Biden's health advisers, the United States is deploying boosters to combat two alarming trends: It appears that vaccine efficacy decreases over time and that two-dose regiments are generally less effective against the delta form. The United States has seen a surge in new cases, hospitalizations, and fatalities this summer and fall, owing to unvaccinated people spreading the virus and increasing the risk of exposure for those who have been vaccinated.

According to the sources, the FDA looked for information on the effectiveness of a third total dose of the Moderna vaccine but is now willing to move forward and consider the half-dose booster that Moderna has offered.

Biden, who received his Pfizer booster on Monday, has stated that the unvaccinated remains a pandemic.

Pfizer and Moderna, according to Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, would eventually be considered three-dose vaccines.

Sites that deliver vaccinations will have to manage several versions as the vaccination campaign expands. In addition to Moderna possibly adding a half-dose booster, Pfizer is requesting approval for a 10-microgram dosage vaccine for children aged 5 to 11, which is one-third the strength provided to those aged 12 and higher.

Fauci has stated that booster shots for Moderna and Johnson & Johnson's one-dose vaccine will be available soon. He told NBC's "Meet the Press" earlier this month, "I believe it will be weeks, not months."