US firm says potential mpox and smallpox vaccine to be tested in Kenya shows promise
Tonix says TNX-801 provides protective immunity to animals with a single-dose
US-based biopharmaceutical company, Tonix Pharmaceuticals, has presented data demonstrating that TNX-801 protected animals from mpox and rabbitpox and was well tolerated, even in immunocompromised animals.
The presentation titled, “A Novel Single-Dose, Attenuated Live, Minimally Replicative Mpox Vaccine”, highlighted positive preclinical efficacy data, the company said after the oral presentation at the World Vaccine Congress Washington 2025, held between April 21-24.
“TNX-801 shows promise as a potential mpox and smallpox vaccine by providing protective immunity to animals with a single-dose,” said Seth Lederman, Chief Executive Officer of Tonix Pharmaceuticals.
“TNX-801 was generally well tolerated, even in immunocompromised animals. The new data show durable six-month protection against a lethal challenge with rabbitpox virus and protection of immunocompromised animals against a lethal challenge with monkeypox clade IIa virus. These new data build upon prior studies showing protection of animals against a lethal challenge with intratracheal clade Ia mpox virus. In all of these studies, after a single dose vaccination, TNX-801 prevented both clinical disease and formation of lesions.”
Dr Lederman continued: “The ongoing clade IIb mpox epidemic that started in 2022, and the more recent and ongoing clade Ib mpox epidemic, highlight the need for additional vaccine options, particularly single-dose options. Both the 2022 clade IIb and the 2024 clade Ib mpox epidemics have been declared by the World Health Organization (WHO) to be Public Health Emergencies of International Concern (PHEICs). We believe TNX-801 has the potential to make an impact towards preventing mpox and controlling future mpox epidemics.”
TNX-801 is a minimally replicative, live-virus vaccine based on synthesised horsepox that has been shown to provide single-dose immune protection against a monkeypox challenge with better tolerability than 20th century vaccinia live-virus vaccines in animals. In September 2024, Tonix announced that the WHO’s preferred target product profile (TPP), released at the WHO sponsored Mpox Research and Innovation Scientific Conference, aligns with the characteristics of TNX-801. Key elements of the WHO draft TPP include single-dose, durable protection, administration without special equipment, and stability at ambient temperature. Other potential beneficial characteristics include the ability to limit forward transmission, use in case-contact vaccination strategies and suitability for use in immunocompromised individuals.
TNX-801 is a single-dose, attenuated, minimally replicative, live virus vaccine based on horsepox in pre-clinical development to prevent mpox and smallpox. Tonix reported positive preclinical efficacy data, demonstrating that TNX-801 vaccination protected non-human primates against lethal challenge with monkeypox.
After a single dose vaccination, TNX-801 prevented clinical disease and lesions and decreased shedding in the mouth and lungs of non-human primates.
The findings are consistent with mucosal immunity and suggest the ability to block forward transmission, similar to Dr Edward Jenner’s vaccine, which eradicated smallpox and kept mpox out of the human population. TNX-801 is based on synthesized horsepox which is believed to be more closely related to Dr. Jenner’s vaccine than 20th century vaccinia viruses.
Smallpox vaccines descended from Jenner’s vaccine used prior to 1900 would be called horsepox by modern nomenclature. TNX-801 is delivered percutaneously with only one dose and therefore may achieve higher rates of community protection than two-dose vaccines by eliminating drop-out between doses and limiting forward transmission. Tonix has received official written response from a Type B pre-Investigational New Drug Application (IND) meeting with the FDA to develop TNX-801 as a potential vaccine to protect against mpox disease and smallpox.
Tonix is collaborating with the Kenya Medical Research Institute (KEMRI) to design, plan and seek regulatory approval for a Phase I clinical study of TNX-801 in Kenya.
The company believes TNX-801 has the potential to make a global impact on mpox and the risk of smallpox because of its durable T-cell immune response, the potential to manufacture at scale, and the use of a lower dose than non-replicating vaccines.
The Federal Drug Administration (FDA)-approved non-replicating mpox vaccine Jynneos requires two doses and provides a relatively short duration of protection. FDA also recently approved ACAM2000, a live, replicating vaccinia vaccine for prevention of mpox. ACAM200 is a clone from DryVax, a 20th century vaccinia vaccine derived from the NYCBH strain. Pre-clinical results from an mRNA vaccine recently showed some protection from a Clade I monkeypox challenge, but with multiple break-through lesions in vaccinated animals.
