Tecovirimat: Safety and Efficacy in Combating Mpox Outbreaks

Mpox, formerly known as monkeypox, is a virus that is spreading and infecting people all over the world, including the United States. Mpox isn't life-threatening for most people, but it can cause severe symptoms and complications in vulnerable individuals, such as children, older adults, and people with a weakened immune system. Tecovirimat, a novel antiviral drug currently FDA-approved only for smallpox, is undergoing clinical trials to assess its efficacy and safety in treating mpox.

This article explores what is known about tecovirimat and its potential for managing mpox outbreaks.

What is tecovirimat?

Tecovirimat is an antiviral drug developed to treat smallpox, a viral infection caused by the same family of viruses — orthopoxviruses — that causes mpox. While there haven't been any reports of smallpox in the United States since 1978, the U.S. has a stockpile of tecovirimat, also called TPOXX or ST-246, because of smallpox preparedness.

Can tecovirimat help with mpox outbreaks?

Mpox is an infection caused by the monkeypox virus. It's a zoonotic disease, meaning it can spread between animals and humans (and also between humans). It's regularly found in parts of Central and West Africa and cases found outside of this area were rare and usually related to travel. However, in 2022, mpox appeared in Europe and the Americas and rapidly spread throughout the world. Shortly after the outbreak, the World Health Organization (WHO) renamed the disease to reduce stigma and discrimination from monkeypox to mpox.

Researchers are now looking at tecovirimat as a potential treatment for mpox, particularly for severe cases. Mpox infections cause a painful blistery rash, fatigue, fever, headaches, muscle aches, and enlarged lymph nodes. The virus spreads through close contact, such as touching or kissing someone who's infected or touching a contaminated object. Symptoms appear within 1–21 days after exposure to the virus and may last 2–4 weeks.

Most people fully recover from mpox. However, those who develop serious mpox symptoms are at risk of developing other infections, like sepsis or pneumonia, that can lead to serious, potentially life-threatening, complications. Finding an effective treatment for mpox is crucial for those at risk of serious symptoms.

Tecovirimat efficacy

It's not known if tecovirimat is a safe and effective treatment for mpox. The CDC has also declared that while studies suggest it might be effective in animals, further testing is needed to determine its safety and effectiveness for humans.

Currently, clinical trials are underway to determine if tecovirimat is an effective mpox treatment. The FDA and CDC encourage doctors to tell their patients diagnosed with mpox about the current clinical trial — Study of tecovirimat for mpox (STOMP). The FDA has streamlined the enrollment process to fast-track the research and get the necessary data to determine if tecovirimat is a suitable treatment for mpox.

A National Institutes of Health (NIH) co-sponsored study evaluated the effectiveness of tecovirimat for mpox in the Democratic Republic of Congo (DRC) where the virus is endemic (always present). Initial results show that the antiviral drug is safe but may not reduce the duration of the infection. However, the mortality rates of participants in the study were lower than the general DRC population infected with mpox. This was true even for participants who didn't receive tecovirimat. The data suggests that more supportive care for people with serious mpox symptoms may lead to better outcomes.

Tecovirimat side effects

Tecovirimat is generally well-tolerated and there have been no reported serious adverse events from the clinical trials. The most common side effects affect less than 2% of people taking the medication.

People with underlying health conditions or those taking other medications may be at risk of side effects. For instance, those taking anti-diabetic medications like repaglinide (oral medication for people with type 2 diabetes) may experience low blood sugar with tecovirimat and should closely monitor their blood sugar levels.

Regulatory approvals

The European Medicines Agency has approved the use of tecovirimat, called tecovirimat SIGA, to treat mpox in the European Union. They based their approval on results from animal studies, showing 80–100% survival in animals treated with tecovirimat after receiving a lethal dose of mpox. However, results from animal studies may not accurately predict human outcomes.

The National Institutes of Health’s (NIH) National Institute of Allergy and Infectious Diseases (NIAID) has sponsored clinical trials to evaluate the safety and efficacy of tecovirimat, but it's not approved for use by the FDA to treat mpox.

Special considerations

Due to FDA regulations, doctors are unable to prescribe tecovirimat to treat patients diagnosed with mpox since it's not an approved use. However, people with the viral infection can get the medication in other ways. As noted above, the CDC and FDA encourage doctors to tell their patients with mpox about the STOMP trial.

Any adult diagnosed with mpox with any of the following conditions or issues will be automatically enrolled in the STOMP trials open-label arm to receive tecovirimat and not a placebo:

• Severe mpox symptoms
• Severe immunodeficiency
• An inflammatory skin condition
• People taking medications that may affect tecovirimat levels
• Pregnant people
• People who are breastfeeding

Children diagnosed with mpox are also eligible for the open-label arm of the STOMP trial to receive the antiviral drug tecovirimat. All other adult participants are randomly assigned to receive tecovirimat or a placebo. All participants receive treatment for 14 days.

People with weakened immune systems or active skin conditions may also be eligible for tecovirimat treatment through the Expanded Access program for compassionate use. This program gives people with serious or life-threatening conditions access to investigational medical treatments not available to the general public.

Bottom line

It's not clear if tecovirimat is an effective treatment for mpox infections. However, it appears to be safe for most people, causing few side effects. For those looking for treatment for mpox, the FDA and CDC have made tecovirimat accessible through the STOMP trial and Expanded Access program.