The Health and Human Services Department has secured 171 million doses of new Covid vaccines that target the omicron variant in preparation for a fall booster campaign.

The U.S. has agreed to purchase 66 million doses of Moderna’s new vaccine formula in a $1.74 billion deal, HHS announced Friday. The Moderna order comes on top of a $3.2 billion agreement to purchase 105 million doses of Pfizer’s updated shots that target omicron.

HHS expects to receive the first deliveries from Pfizer and Moderna early this fall. The new vaccines that target omicron still need to be authorized by the Food and Drug Administration and cleared by the Centers for Disease Control and Prevention.

The FDA last month told Pfizer and Moderna to develop vaccines with a new formula that targets the omicron BA.4 and BA.5 subvariants in addition to the original strain of Covid that first emerged in Wuhan, China, in 2019.