By Ahmed Aboulenein and Michael Erman

(Reuters) -Around 4 million Americans received the updated COVID-19 shots in September, according to the U.S. Department of Health and Human Services (HHS), even as some people have found it difficult to book vaccination appointments or find the vaccines at no cost.

“The Biden-Harris Administration, through HHS, has been working directly with manufacturers and distributors to ensure that the vaccines are getting to pharmacies, hospitals, clinics, and other vaccination sites, including long-term care facilities as quickly as possible,” a spokesperson for the department said in an emailed statement.

The updated shots from Pfizer and BioNTech or Moderna are single-target vaccines aimed at the XBB.1.5 Omicron subvariant of the coronavirus, which was dominant in the U.S. for much of this year but has since been overtaken by other variants as the virus evolves.

Another updated COVID shot, made by Novavax, was authorized on Tuesday but is not yet available.

Rollout of the Pfizer and Moderna shots began in earnest after the U.S. Centers for the Disease Control and Prevention (CDC) recommended them on Sept. 12. The rollout of last year’s updated shots targeting two virus variants started about 10 days earlier, and by Sept. 21, around 4.4 million Americans had rolled up their sleeves for one of them.

U.S. public health officials have expressed hope that Americans will welcome the new vaccines as they would an annual flu shot. But demand for COVID vaccines has dropped sharply since 2021, when they first became available.

Around 56.5 million people, or 17% of the U.S. population, received last year’s version of the vaccines.

(Reporting by Ahmed Abouelnein in Washington and Michael Erman in Maplewood, NJ; Editing by Bill Berkrot)