"We are expecting that they (the U.S. Biomedical Advanced Research and Development Authority (BARDA)) have a desire to expand the emergency stock for the smallpox vaccine and therefore we also expect to see more contracts in the future," Chief Financial Officer Ole Larsen told Reuters.

The Danish biotech said late on Wednesday it had won an order for its freeze-dried smallpox vaccine worth potentially $539 million(403.38 million pounds).

The deal was an important confidence boost for the firm, just weeks after one of its key drug candidates suffered a major setback.

(Reporting by Stine Jacobsen, editing by Terje Solsvik)