The European Medicines Agency’s Committee for Medicinal Products for Human Use (CHMP) has recommended that Tecovirimat SIGA should no longer be used for the treatment of mpox.

A review of the antiviral medicine was initiated at the request of the European Commission following evidence from clinical trials suggesting a lack of effectiveness in the treatment of mpox. The CHMP’s decision does not affect the drugs other uses, including in the treatment of smallpox, cowpox, and complications from smallpox vaccines. 

Two studies supported by the US National Institute of Allergy and Infectious Diseases found that the antiviral did not reduce the duration of mpox lesions among children and adults with clade I mpox in the Democratic Republic of the Congo and did not reduce the time to lesion resolution or have an effect on pain among adults with mild to moderate clade II mpox.

Preliminary results from a third study also did not indicate faster skin lesion resolution compared with placebo, and a fourth trial found no benefit of the antiviral for the time taken for mpox skin blisters to scab over and heal completely. 

The CHMP’s decision was built on a review of the four randomized, placebo-controlled, double-blind clinical trials in addition to an assessment of all other available data on the benefits and risks of Tecovirimat SIGA and consultations with experts in infectious disease. 

The committee did not find any new safety concerns.

Tecovirimat SIGA was authorized under “exceptional circumstances: in January 2022 to treat mpox, smallpox, and cowpox in adults and children weighing at least 13 kg. 

At the time of approval, it was not possible to carry out studies in infected people, as the viruses rarely circulated. Smallpox, mpox, and cowpox are either eradicated or occur only sporadically in the EU. The approvals of Tecovirimat SIGA for mpox, smallpox, cowpox, and complications from smallpox vaccines were based on results from an animal model of mpox infection that demonstrated antiviral activity and a survival benefit when treatment was started early. 

The subsequent human studies were made possible following a World Health Organization declaration of two public health emergencies of international concern in response to mpox global outbreaks. 

There are no other medicines authorized in the EU for treating mpox infections. Patients who have already started treatment with Tecovirimat SIGA can complete their treatment course, the CHMP said. 

The CHMP said the in vitro and animal data presented at the time of marketing authorization are still considered relevant for the use of the antiviral in treating smallpox, cowpox, and complications from smallpox vaccines. The restriction is limited to the use of Tecovirimat SIGA in mpox because the expected context of use and the disease courses of smallpox, cowpox, and complications from smallpox vaccines are each different from those of mpox.