Just as a new strain of mpox spreads across Africa, results from a preliminary analysis of a study that began during the 2022 viral outbreak stands to provide more clarity on the clinical benefit of SIGA Technologies’ smallpox antiviral Tpoxx.
The treatment did not meet the trial's primary endpoint of reducing patients' time to lesion resolution within a 28-day treatment period, the National Institutes of Health’s (NIH) National Institute of Allergy and Infectious Diseases (NIAID) reported. The PALM 007 study enrolled patients in the Democratic Republic of the Congo (DRC).
However, a “meaningful improvement” was seen in patients whose symptoms started seven days or fewer before study randomization and in those with severe or greater disease, which is defined as having 100 or more skin lesions. The “maximum benefit” in certain groups supports SIGA’s view that post-exposure prophylaxis will be “vital” for smallpox and severe mpox treatment, chief scientific officer Dennis Hruby said in a Thursday release.
Overall, SIGA is “highly encouraged” by the results, CEO Diem Nguyen added.
“Missing the primary endpoint is not entirely unexpected given that the study population was hospitalized during the duration of treatment receiving a high level of supportive care, and since many presented for treatment more than a week after their illness started,” Nguyen explained.
The controlled hospital environment may have played a role in the trial's comparator group data, the company noted. Patients were hospitalized for the duration of the study to ensure access to food and proper data collection, therefore receiving a level of care unavailable to “most” mpox patients in real-world situations, according to SIGA.
Compared with other observational studies from the DRC that were used to plan the trial, patients in the placebo arm of the recent trial had “much more” favorable outcomes, which may have reduced the measured benefit of Tpoxx.
Now, the company and trial sponsor NIAID are further analyzing the data to collect a greater understanding of the results and the “potential implications." Additional studies include four randomized trials enrolling in the U.S., Europe, Canada and Switzerland, Brazil and Argentina. Those trials differ in “significant respects” to the DRC trial, including on factors such as a patient population.
Meanwhile, the U.S. just picked up an additional $113 million worth of Tpoxx in the latest in a series of supply deals over recent years. Tpoxx made waves as the first FDA-approved treatment for smallpox in 2018 and further picked up steam as a mpox treatment in 2022. Still, back in 2022 the FDA began urging doctors to be “judicious” in writing Tpoxx prescriptions due to the rapidly evolving nature of the virus that could leave the treatment ineffective.
The World Heath Organization (WHO) yesterday declared the latest mpox outbreak in Africa a global health emergency after a deadlier stain of the virus spread to four previously unaffected African countries. More than 17,000 cases and more than 500 mpox-related deaths have been reported in 13 countries across Africa since Jan. 1, according to the Africa Centers for Disease Control and Prevention.