The U.S. Department of Health has modified its smallpox vaccine contract with Bavarian Nordic to support a Phase III study that is larger than initially proposed. The procurement contract for the prophylactic smallpox vaccine candidate Imvamune has risen by $32 million to $544 million. Bavarian Nordic is facing additional costs prior to starting the trial, which will have 4,000 participants; enrollment will start in 2013. Under the terms of the contract, the government is stockpiling 20 million doses of Imvamune under a Project BioShield contract, and it has already received the first 8 million doses. Imvamune is based on a live nonreplicating MVA-BN virus, and Bavarian Nordic is selling it to governments as a vaccine in development.