Abigail Erwin, University of Manitoba

Abigail J. Erwin1, Hannah L. Wallace1, Morgan R. Hiebert1, Jason Kindrachuk1,2 1Medical Microbiology & Infectious Diseases, Max Rady College of Medicine, University of Manitoba 2National Microbiology Laboratory, Public Health Agency of Canada

Fighting & Responding

Background: Human mpox is an emerging zoonotic disease caused by monkeypox virus (MPXV) of the orthopoxvirus (OPXV) genus. Infections range from asymptomatic to fatal and due to expansion of mpox cases, WHO declared public health emergencies of international concern in both 2022 and 2024. Orthopoxviruses are closely related, with high antigenic similarity, a fact that has been leveraged for previous OPXV vaccine development. The third-generation vaccine, MVA-BN, uses replication-incompetent Vaccinia virus (VACV), with a 35-85% efficacy rate for protection against mpox. However, the need for vaccines with increased effectiveness and availability in endemic regions remains. We propose a multivalent self-amplifying (sa)RNA vaccine targeting OPXVs. SaRNA encodes proteins for RNA replication and antigens, enhancing potency and durability at lower doses. Methods: Single-valent and multi-valent vaccine constructs encoding MPXV-specific and universal OPXV antigens were tested in vitro and in vivo. Mice received two doses of saRNA vaccine or PBS control, 4 weeks apart, before challenge with VACV or MPXV. Plasma collection is used to detect anti-OPXV IgG and immune markers, which help assess vaccine immunogenicity. Tissue pathology and immunohistochemistry are performed at sacrifice to evaluate organ health and immune response. Results: Vaccine constructs were tested in vitro and demonstrated expression via immunofluorescence and western blotting, confirming molecular weights of full protein translation. Single-valent vaccines are currently being tested in vivo, and preliminary results indicate that the constructs are well tolerated in BALB/C mice. Results to follow. Conclusion: Given other studies using saRNA vaccines, we expect high vaccine efficacy with appropriate safety profiles.