WASHINGTON -- The Biden administration said Friday it has reached an agreement with Moderna to buy 66 million doses of the company's next generation of COVID-19 vaccine that targets the highly transmissible Omicron variant, enough supply this winter for all who want the upgraded booster.

The order of the bivalent shot follows the announcement last month that the federal government had secured 105 million doses of a similar vaccine from rival drugmaker Pfizer. Both orders are scheduled for delivery in the fall and winter, assuming regulators sign off on their effectiveness. The Pentagon said the Moderna contract was worth US$1.74 billion.

The Omicron strain has been dominant in the U.S. since December, with the BA.5 subvariant now causing a massive wave of infections across the country, even infecting U.S. President Joe Biden.

"We must stay vigilant in our fight against COVID-19 and continue to expand Americans' access to the best vaccines and treatments," Health and Human Services Secretary Xavier Becerra said in a statement. "As we look to the fall and winter, we're doing just that -- ensuring Americans have the tools they need to stay safe and help keep our nation moving forward."

The U.S. orders with Pfizer and Moderna include options to purchase 300 million doses each, but reaching that total will require more funding from Congress, the Biden administration said.

About 261 million Americans have received at least one COVID-19 shot, but only 108 million have received a booster.