Though smallpox was declared eradicated in 1980, there have been concerns the contagious and sometimes fatal disease could be used as a bioweapon.

So the U.S. Food and Drug Administration on Friday approved the first drug that could treat it.

“To address the risk of bioterrorism, Congress has taken steps to enable the development and approval of countermeasures to thwart pathogens that could be employed as weapons. Today’s approval provides an important milestone in these efforts,” FDA Commissioner Scott Gottlieb said in a statement.

The drug, TPOXX (tecovirimat) was tested on animals infected with viruses closely related to the virus that causes smallpox, and the safety was evaluated in 359 healthy human volunteers without a smallpox infection. Side effects reported included headache, nausea and abdominal pain.

The variola virus — which causes smallpox — was mainly spread through direct contact between people. Symptoms that would show up 10 to 14 days after infection included fever, exhaustion, headache and backache, as well as a rash of small pink bumps that would progress to pus-filled sores, crust over and scar. The infection could lead to inflammation of the brain, corneal ulcerations and blindness.