SIGA Technologies Inc. /zigman2/quotes/201166334/composite SIGA -0.21% rose 9.6% in Friday afternoon trade on the Food and Drug Administration's approval of its TPOXX, the first-ever smallpox therapy. The contagious and often-deadly disease -- described as "one of the world's most devastating diseases known to humanity" by the World Health Organization -- has been considered eradicated since 1980 due to global immunization, but there have been fears that it could be used for bioterrorism, the FDA said. TPOXX was the first drug to receive a "Material Threat Medical Countermeasure priority review voucher," which comes with various incentives for the drugmaker; the drug also received other special designations intended to encourage development of important drugs. To establish the product's safety, it was tested in 359 healthy humans who did not have smallpox, while the efficacy findings that the approval was based on were in animals. These types of approvals are allowed under the FDA's Animal Rule, used in cases when "it is not feasible or ethical to conduct efficacy trials in humans," the FDA said. SIGA shares have surged 9.1% over the last three months, compared with a 5.5% rise in the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.98% and a 2.7% rise in the Dow Jones Industrial Average /zigman2/quotes/210598065/realtime DJIA +0.70% .