Trials for monkeypox antiviral, fractional vaccine dosing launch

Black and orange capsule in gloved hand
Black and orange capsule in gloved hand

Aleksandr Zyablitskiy / iStock

As countries contend with more and more monkeypox cases, UK and US officials have announced the launch of clinical trials to gauge how effective the antiviral drug tecovirimat, known as Tpoxx, is for treating the disease, and to establish how protective intradermal fractional doses of the Jynneos vaccine are against monkeypox.

In addition, Brazil has confirmed 77 cases of the poxvirus in children, and Spain becomes the latest country to initiate fractional vaccine dosing.

US, UK Tpoxx trials to each enroll 500

Yesterday the National Institute of Allergy and Infectious Diseases (NIAID) tweeted that it was launching clinical trials for both tecovirimat and Jynneos in the coming weeks.

The NIAID will start a clinical trial of tecovirimat in September in collaboration with the AIDS Clinical Trials Group. Plans are to enroll more than 500 patients.

The agency is also collaborating with the National Institute for Biomedical Research to initiate a clinical trial of tecovirimat in adults and children with monkeypox in the Democratic Republic of the Congo. This trial was planned before the current outbreak, the NIAID said.

In the United Kingdom, the National Institute for Health and Care Research (NIHR) announced a separate clinical trial of tecovirimat, called PLATINUM (for placebo-controlled randomized trial of tecovirimat in non-hospitalised monkeypox patients).

"Monkeypox is a distressing and sometimes dangerous infection. For the benefit of current and future patients worldwide who have been diagnosed with monkeypox, we need definitive evidence that tecovirimat is safe and effective," lead investigator Sir Peter Horby, PhD, said in a press release.

"Although the early data on tecovirimat are promising, only a randomised clinical trial will provide the level of evidence we need to treat patients with confidence. PLATINUM will provide that evidence."

The UK study plans to enroll 500 or more patients who will either be given a 14-day course of the antiviral (2 daily doses of 600 milligrams) or a placebo. The participants will take the medication at home, and the primary outcome will be the rate at which skin and mucosal lesions heal, and the rate at which throat and lesion swabs test negative for the virus.

Study shows Tpoxx well tolerated

In related news, today JAMA published a research letter on the compassionate use of tecovirimat in 25 monkeypox-confirmed patients seen at University of California-Davis this summer.

All participants were men, with a median age of 40.7 years. Nine had HIV, 1 had a smallpox vaccine more than 25 years earlier, and 4 had received one dose of Jynneos after symptom onset.

Oral tecovirimat was well tolerated by all patients with monkeypox infection, with minimal side effects, the authors said. Ten patients had complete resolution of lesions by day 7 of therapy, while 23 (92%) had resolution of lesions and pain by day 21.

"No control group was included, limiting conclusions of antiviral efficacy pertaining to duration of symptoms or severity," the authors cautioned, however. "Time from symptom onset to presentation was variable among patients, and conclusions related to antiviral use vs natural evolution of disease should be made with caution."

Yesterday the Centers for Disease Control and Prevention (CDC) released demographic information on patients who have received Tpoxx in the United States. The median age of patients is 37 years, 98.9% are men, and Whites (40%) are the largest ethnic group to have received it.

Overall, however, Blacks and Hispanics make up about 65% of US monkeypox cases. The CDC also published new data from a behavioral survey to stop the spread of the virus. It shows that 48% of men who have sex with men say they are reducing their number of sexual partners, 50% are reducing the number of one-time sexual encounters, and 49% are reducing sex with partners met at sex clubs or on dating apps. Results were based on an online survey.

In total, the nation has 15,433 monkeypox cases, the most of any country in the world. And Wyoming, which had been the only state to not report a case, confirmed its first case in a resident of Laramie County.

Brazil reports 77 cases in kids

In other global developments, Brazilian officials have confirmed 77 monkeypox cases in those 18 years and under, with more than a quarter of those in children 4 years and under. 

Yesterday, health authorities in Spain approved the use of fractional, intradermal dosing of the monkeypox vaccine, which will stretch supplies in one of the hardest-hit countries in Europe. Fractional dosing is currently used in the United States and Britain.

Intradermal injections go into the upper layers of the skin, as opposed to just beneath the skin layers or into the muscle.

Spain currently has more than 6,000 cases, and the goal total has eclipsed 40,000 cases.

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