The US Food and Drug Administration (FDA) has approved the first drug indicated for the treatment of smallpox.

Tecovirimat (TPOXX)—a small molecule antiviral therapy developed in conjunction with the US Department of Health and Human Services’ (HHS) Biomedical Advanced Research and Development Authority (BARDA)—has been approved for the US market under the FDA’s Animal Rule, which allows for efficacy results from qualified animal studies to support a drug approval when human trials would be considered unethical.

Under Project Bioshield, BARDA had previously announced the acquisition of 2 million courses of oral TPOXX, which have been delivered to the Strategic National Stockpile (SNS).

FDA commissioner Scott Gottlieb, MD, said tecovirimat provides more assurance versus public concern of potential bioterrorism involving smallpox.

“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,” Gottlieb said in a statement. “Today’s approval provides an important milestone in these efforts.”

In May, an FDA panel had announced a unanimous 17-0 vote in favor of a benefit-risk analysis of the therapy.

With its approval, tecovirimat became the first product to be awarded a Material Threat Medical Countermeasure priority review voucher, Gottlieb said. Its application was previously granted Fast Track and Priority Review designations, and an Orphan Drug designation with its approval.

Its approval was backed by trials reporting its efficacy in animal models infected with viruses closely related to the smallpox virus, and a trial reporting its safety in 359 healthy human volunteers without the virus.

In the animal trials, researchers measured for subject survival at the end of the studies. They reported that more animals administered tecovirimat had survived, versus those treated with placebo. In the human safety trials, the most frequently reported side effects were headache, nausea and abdominal pain.

Smallpox is brought on by the variola virus, which was capable of spreading through direct contact between people. Its symptoms are fever, exhaustion, headache, and backache within 10-14 days of infection, as well as a rash of small, pink bumps that could develop into sores.

Complications commonly associated with smallpox included encephalitis, corneal ulcerations, and blindness.

Though the World Health Organization (WHO) had declared smallpox an eradicated disease in 1980, concern over its use as a bioweapon has persisted. Some of that concern may be quelled with tecovirimat’s approval.

“Today’s action reflects the FDA’s commitment to ensuring that the US is prepared for any public health emergency with timely, safe and effective medical products,” Gottlieb said.