More than 7 million Americans had rolled up their sleeves for the updated COVID-19 vaccines as of Wednesday, according to the U.S. Department of Health and Human Services, despite reports that some people are still finding it difficult to book vaccination appointments or find the shots at no cost.

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

Millions of doses of another updated COVID vaccine from Novavax have also been made available to Americans this week, according to the company.

Distribution of the Pfizer and Moderna shots began after the U.S. Centers for the Disease Control and Prevention recommended them on Sept. 12.

Last year's booster targeting the original virus and another variant was rolled out about 10 days earlier. By Sept. 28, 2022, almost 7.6 million Americans had received the updated shots.

U.S. public health officials have been optimistic that Americans will get the new vaccines and have recommended that everyone ages 6 months and older receive one.

But demand has dropped sharply since 2021, when the shots were first introduced at the height of the pandemic.

About 17% of the U.S. population, or 56.5 million people, ultimately received last year's version of the vaccines.

(Reporting by Patrick Wingrove Editing by Bill Berkrot)