Efforts are underway to study the possibilities of oral smallpox treatment TPOXX as a post-exposure prophylactic (PEP), with the announcement of clinical trials by SIGA Technologies, Inc. last week.
These trials will support a U.S. Food and Drug Administration (FDA) label expansion for the drug, approved for its current use in 2018. Two studies will likely be initiated this year. The first will compare immune responses to the Jynneos smallpox vaccine against the immune response with Jynneos while on TPOXX treatment to determine if TPOXX interferes with the development of immune responses to the vaccine. A second study will focus on developing an expanded safety dataset to undertake 28-day TPOXX doses for PEP indication, compared against the approved smallpox treatment indication, which is 14 days.
“The use of TPOXX for post-exposure prophylaxis has always been an important opportunity for TPOXX use in an outbreak of smallpox,” Dr. Phil Gomez, CEO of SIGA, said. “This was highlighted by the U.S. Government during our initial 2011 procurement and discussed extensively at our FDA Advisory committee meeting in 2018, where TPOXX received a unanimous vote to recommend approval for treatment of smallpox. The COVID-19 pandemic has also shown vaccine hesitancy is a real issue for pandemic response, and the balance of vaccines and anti-viral drugs in stockpiles must be reevaluated in light of current experience.”
The commercial-stage pharmaceutical company has worked with the U.S. Department of Defense’s Joint Program Executive Office for Chemical, Biological, Radiological and Nuclear Defense (JPEO-CBRND) to develop the PEP indication under an approximately $26 million research and development contract. This was meant to counter military concerns about smallpox’s potential use as a bioweapon.
TPOXX was originally authorized by the FDA as a smallpox treatment specifically to neutralize the impact of a potential outbreak or terror attack. In the years since, it has been similarly approved by Health Canada and the European Medicines Agency. In the latter case, initiated earlier this year, the treatment was granted its broadest indication thus far, as it can be used to treat smallpox, monkeypox, cowpox, and complications from vaccination for smallpox.