UC San Diego joins national monkeypox treatment trial

A colorized electron micrograph of monkeypox particles (orange) within an infected cell (brown)
An image provided by the National Institute of Allergy and Infectious Diseases shows a colorized electron micrograph of monkeypox particles (orange) within an infected cell (brown).

The study will try to determine whether the drug tecovirimat is safe and effective against monkeypox.


UC San Diego will be one of several sites across the country studying the efficacy of the drug tecovirimat as a potential treatment for human monkeypox.

Tpoxx, as the drug is marketed, is an antiviral currently approved by the U.S. Food and Drug Administration to treat human smallpox caused by the variola virus, but its safety and effectiveness against monkeypox are unknown.

The new study is a randomized, placebo-controlled, double-blind trial funded by the National Institute of Allergy and Infectious Diseases and led by the AIDS Clinical Trial Group. The AntiViral Research Center at the UCSD School of Medicine is part of the group.

“There is an urgent need for [monkeypox] treatments, and this study will help us determine whether tecovirimat should be one of them,” said Dr. Susan Little, a professor of medicine at UCSD and an infectious-disease specialist at UCSD Health who is co-director of the AntiViral Research Center and a lead investigator for the UCSD trial.

“People living in the San Diego region who have confirmed or probable mpox have the opportunity to make a huge contribution by participating in this study,” Little said.

The current monkeypox outbreak emerged in the spring and has spread throughout the world, with more than 75,000 cases in over 100 countries and more than 28,000 cases in the United States. San Diego County had recorded 440 cases as of the most recent data.

The virus belongs to the same family of viruses as variola. Mpox symptoms are similar to smallpox but milder, and mpox is rarely fatal. Mpox is not related to chickenpox.

The new trial, with more than 60 sites, will enroll more than 500 adults with monkeypox virus infections. It will include people with or at high risk of severe disease, including those who are pregnant or breastfeeding, along with children and those with underlying immune deficiency and active inflammatory skin conditions, who will receive open-label tecovirimat, according to a statement from the university.

All participants in the trial will be followed for at least eight weeks through a combination of virtual and in-person visits and daily self-reports to determine whether those receiving tecovirimat heal more quickly compared with those receiving the placebo. The study also will provide data on the optimal dosing and safety of tecovirimat in children and people who are pregnant or breastfeeding.

Monkeypox was first identified in 1958 and has caused an increasing number of infections annually in endemic countries, primarily portions of Africa. The current outbreak has been characterized primarily by increased person-to-person transmission. According to the U.S. Centers for Disease Control and Prevention, close contact during sexual activity is believed to play an important role in the outbreak.

Most cases have been reported among men who have sex with men. But men who have sex with women also have been infected, as have women and children. There currently are no therapies approved to treat human monkeypox. ◆