Tonix gives update on development of its single-dose live attenuated virus vaccine candidate for Mpox

Tonix Pharmaceuticals, a biopharmaceutical company, aims to advance the development of its live attenuated virus vaccine, TNX-801 (recombinant horsepox virus), for preventing mpox and other infectious diseases. On August 14, 2024, the World Health Organization (WHO) determined that the upsurge of mpox in a growing number of countries in Africa constitutes a public health emergency of international concern, the second such declaration in the past two years called in response to an mpox outbreak. The current outbreak was caused by Clade I monkeypox virus, while the 2022 outbreak was Clade II monkeypox virus.

TNX-801 is a live replicating attenuated vaccine candidate based on horsepox that is believed to provide immune protection with better tolerability than the 20th-century vaccinia viruses. The same vaccine platform upon which TNX-801 is based was selected by the US National Institutes of Health (NIH) for Project NextGen for an engineered version that expresses the spike protein of SARS-CoV-2.

As previously disclosed, TNX-801 protected animals against lethal challenge with intratracheal Clade I monkeypox virus. After a single-dose vaccination, TNX-801 prevented clinical disease and lesions and also decreased shedding in the mouth and lungs of non-human primates. These findings are consistent with mucosal immunity and suggest the ability to block forward transmission, similar to Dr Edward Jenner’s vaccinia vaccine, which eradicated smallpox and kept mpox out of the human population.

Seth Lederman, CEO, Tonix, said, “Preclinical trials demonstrate that TNX-801 combines immune protection with improved tolerability and safety compared to other vaccines based on orthopoxviruses, and is administered with a single dose which has advantages over two-dose regimens. The durability of protection from 19th-century live virus vaccinia vaccines suggests that our attenuated TNX-801 will not require multiple repeated doses at six-month intervals like mRNA vaccines. Also, the stability of live virus vaccines eliminates the need for ultra-cold storage which complicates the widespread use of mRNA vaccines in Africa, where they are needed most right now.”

The global mpox outbreak, which commenced in 2022, has affected over 90,000 persons in countries where mpox had previously not been endemic, including Europe and the US The spread of Clade IIb strain mpox in 2022 underscores the pandemic potential of mpox. Unlike Clade IIb mpox, the Clade I strain of mpox appears to be spreading to countries neighbouring the Democratic Republic of the Congo. Clade I mpox is typically associated with approximately 20 times the case fatality rates than Clade IIb mpox in Africa. According to the US CDC, and other experts, there is a significant risk that the deadlier Clade I strain may appear in the US.

Further, the Bipartisan Commission on Biodefense recently highlighted the renewed dual threats of a more virulent mpox epidemic and a smallpox re-introduction from lab accidents or bad actors. The National Academies of Science, in its review of smallpox preparedness, highlighted the need for new single-dose vaccines, like TNX-801 against smallpox.