Ahead of a planned booster vaccination campaign this fall, the U.S. government has locked up supply of Moderna Covid-19 vaccines designed to protect against both the original strain of the virus as well as the omicron subvariants that are now circulating widely.

According to terms announced Friday, Moderna will supply the government with 66 million doses of its booster vaccine candidate. The contract includes the option to purchase up to 234 million booster doses. Moderna could be paid up to $1.74 billion, depending on how many doses are ordered.

The Moderna vaccine, named Spikevax, received FDA approval in January for those 18 and older. That vaccine was designed to address the original strain of the novel coronavirus. The company has also been developing two different booster candidates, each a bivalent vaccine that protect against two different strains. Both of these new vaccines will protect against the original strain. One of them, mRNA-1273.222, will also contain the BA.4/5 omicron strain that is dominant in the U.S., consistent with booster guidelines that the FDA set last month. The second booster candidate, mRNA-1273.214, addresses the BA.1 subvariant, which may be more applicable to other regions in the world.

The contracted supply of Moderna boosters is in addition to the agreement the government struck for 105 million bivalent booster doses of the Pfizer/BioNTech Covid-19 vaccine, plus the option to purchase up to 195 million additional doses. Both boosters will need FDA authorization and a recommendation from the Centers for Disease Control and Prevention. If these new shots pass muster with both agencies, they could be ready to go into arms in early fall, the Department of Health and Human Services said. Citing unnamed sources, The New York Times reported that the Biden administration plans to offer the updated Covid-19 shots in September.

As of now, boosters have FDA authorization for those 50 and older as well as those 12 and older who have conditions that impair their immune systems. The Times reported that due to the rising number of Covid-19 cases, some federal health officials advocated for broadening booster eligibility of the current vaccine ahead of the rollout of the retooled versions. But after the companies assured government officials that they could deliver their bivalent boosters by mid-September, the FDA and CDC decided it would be better to focus on the fall vaccination campaign with the new versions of the shots, the Times reported.

According to the CDC, 603.7 million vaccine doses have been administered in the U.S. The agency calculates that 78.8% of the U.S. population has received at least one dose and 67.2% of the population is fully vaccinated (defined as those who have received the second dose of a two-shot vaccine or one dose of the single-shot Johnson & Johnson vaccine). Of those who are fully vaccinated, the CDC reports that 107.9 million people have received a booster shot. More than half of the total booster-eligible population has yet to receive a booster shot, the CDC’s latest data show.

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