Monkeypox appears in rashes all over the body.

There is only one drug meant to treat monkeypox, Tpoxx. But recently, United States health officials said even a small mutation in the virus could render Tpoxx ineffective and are warning against overuse of the drug.

The Food and Drug Administration updated its guidance this week for Tpoxx, which has been prescribed to tens of thousands of patients with the monkeypox virus.

In an online update, FDA officials cautioned that a single molecular change to monkeypox “could have a large impact on the antiviral activity of Tpoxx.” Since viruses are constantly evolving to overcome obstacles to infection, including drugs, regulators stressed that doctors should be “judicious” in prescribing the medication.

Meanwhile, the Centers for Disease Control and Prevention last Thursday said Tpoxx should no longer be given to otherwise healthy adults who are not suffering severe symptoms.

The primary hallmark of the virus is the rash, or “pox,” that infected individuals develop. Other symptoms include fever, chills and swelling of the lymph nodes. Monkeypox is spread via close skin-to-skin contact with an infected individual or by contact with infected body fluids on surfaces; the virus can live on surfaces for up to 15 days.


The monkeypox vaccine booster is available in the United States and has been in distribution since the end of July.

“For most patients with healthy immune systems, supportive care and pain control may be enough,” agency officials said in a statement.

The moves to scale back Tpoxx’s use follow weeks of criticism from HIV advocates and other patient groups who have urged the Biden administration to make the antiviral drug more widely available. Tpoxx is approved for the related smallpox virus, and its use against monkeypox is considered experimental and tightly controlled by federal officials.

Doctors wishing to prescribe the drug must submit an application to the CDC documenting their patient’s needs and agreeing to track their results and any side effects. Officials have shipped 37,000 courses of the drug to physicians.

The update came as federal officials recently expressed cautious optimism about the trajectory of the outbreak, noting that new cases have fallen about 50% since their peak in August.

Dr. Anthony Fauci, the nation’s top infectious disease official, noted that resistance is always a risk when using antiviral drugs.

“That’s why we’re uncomfortable when you only have a single drug,” Fauci told reporters.

He added that a recently launched study of Tpoxx supported by the National Institutes of Health will track signs of mutation that could lead to resistance. The study is expected to enroll more than 500 patients across 60 U.S. sites.

Last month, the Biden administration invoked rare emergency powers to stretch the nation’s limited supply of monkeypox vaccine. And last week a separate declaration expedited the use of experimental tests for the virus.

But no changes were made to allow emergency use of Tpoxx, stoking complaints from groups representing gay and bisexual men, who have been most vulnerable to the outbreak.

The U.S. government’s national stockpile contains has more than 1.7 million courses of Tpoxx, originally manufactured for use during a potential bioterrorism attack.

The FDA approved the medication in 2018 under its “animal rule,” which allows approval based on animal data when human testing is unethical or unfeasible.

“Without human trials, we don’t know if Tpoxx is beneficial for humans with monkeypox,” FDA Commissioner Dr. Robert Califf told Senate lawmakers at a hearing this week.

The CDC reported last week that 3.5% of patients tracked through its Tpoxx program reported side effects, mainly headache and nausea. It recommends getting the monkeypox vaccine when you are eligible, and communicating openly with close contacts and medical professionals if you or those you are close with developing symptoms of the disease.

Stacker is collecting data from the CDC to examine monkeypox case trends state by state. Numbers for Florida are as follows:

Cumulative cases since July 2022: 2,126

Cumulative cases per million people: 97.6

New cases during the last 7 days: 256

New cases per million people: 11.8

On Aug. 4, 2022, the Biden administration declared monkeypox a public health emergency. Since then, every state and Washington, D.C., has recorded cases of the virus.