The U.S. government has reached a deal with Moderna to buy 66 million doses of the biotechnology company’s updated COVID-19 booster shot this year, promising up to $1.74 billion in exchange.

The agreement includes an option for the U.S. to purchase another 234 million doses of the booster, which contains both the original coronavirus strain as well the prevailing omicron subvariant BA.4/5.

The supply contract comes after Moderna developed another bivalent shot that contained the original omicron variant BA.1. Moderna hoped to push out this booster in the summer following study results that showed strong immune responses to omicron.

While both Moderna’s and Pfizer’s existing COVID-19 vaccines still offer substantial protection against the disease’s worst outcomes, omicron can more readily evade the immunity that the shots provide, particularly versus infection.

Initial research has suggested the omicron BA.4/5 strain can evade protection as well, even from antibodies generated by infection by the BA.1 omicron strain. In June, the Food and Drug Administration recommended vaccine boosters include the BA.4/5 strain ahead of fall and winter.

According to the Centers for Disease Control, the currently prevailing strain as of July 23 is BA.5. COVID-19 cases across the country have been rising along with hospitalizations and deaths, but are nowhere near levels seen in the winter of 2021.

The FDA has been preparing for a booster shot campaign in September before the winter, when COVID-19 cases are expected to rebound, according to The New York Times. The U.S. government previously paid Pfizer and BioNTech $3.2 billion to secure 105 million doses of the vaccine. Pfizer is planning to advance a BA.4/5 modified shot ahead of the planned booster rollout this fall.

Eligibility for second boosters is currently limited to people over the age of 50 or who have certain health conditions and are older than 12. According to The New York Times, the FDA is planning to expand eligibility to include all adults and possibly children during the booster campaign.

The U.S. government still encourages those who are eligible to get a booster if they have not yet done so.