Different immunogens and prime-boost vaccination strategies affect the efficacy of recombinant candidate vaccines against pathogenic orthopoxviruses.

Although not as lethal as variola virus (VARV), the cause of smallpox, monkeypox virus (MPXV) represents a threat to public health, with important infection rates and mortality in several African countries and signs of spreading worldwide. MPXV may establish new reservoirs in non-endemic countries and can be considered a possible biological weapon. Human-to-human MPXV transmission is increasing with a growing susceptibility, coincident with the declining herd immunity against smallpox. The emerging threat of MPXV highlights the urgent need for protection from new zoonotic infections, as mankind is completely unprepared for encounters with new viruses. Preventive vaccination remains the most effective control against orthopoxviruses (OPXVs) such as MPXV and prime-boost vaccination strategies can significantly influence vaccine efficacy and enhance immune responses. Our study aimed at characterizing potential vaccine candidates against OPXV infections in a murine model using DNA, viral and protein recombinant vaccines using different prime-boost regimens. The experiments employed Vaccinia virus (VACV) A33, B5, L1, and A27 envelope proteins as immunogens for both priming and boosting. Priming was carried out using a mixture of four plasmids (4pVAXmix), and boosts employed fowlpox (FWPV) recombinants (4FPmix) and/or the purified recombinant proteins (4protmix), all of them expressing the same antigens. One or two doses of the same immunogens were tested and identical protocols were also compared for intranasal (i.n.) or intramuscular (i.m.) viral administration, before challenge with the highly pathogenic VACV VV