Evaluation of the efficacy of modified vaccinia Ankara (MVA)/IMVAMUNE® against aerosolized rabbitpox virus in a rabbit model

Infection of rabbits with aerosolized rabbitpoxvirus (RPXV) produces a disease similar to monkeypoxand smallpoxin humans and provides a valuable, informative model system to test medical countermeasures against orthopoxviruses. Due to the eradication of smallpox, the evaluation of the efficacy of new-generation smallpox vaccinesdepends on relevant well-developed animal studies for vaccine licensure. In this study, we tested the efficacy of IMVAMUNE® [Modified VacciniaVirus Ankara-Bavarian Nordic (MVA-BN®)] for protecting rabbits against aerosolized RPXV. Rabbits were vaccinated with either phosphate-buffered saline(PBS), Dryvax®, a single low dose of IMVAMUNE®, a single high dose of IMVAMUNE®, or twice with a high dose of IMVAMUNE®. Aerosol challenge with a lethal doseof RPXV was performed 4 weeks after the last vaccination. All PBS control animals succumbed to the disease or were euthanized because of the disease within 7 days postexposure. The rabbits vaccinated with Dryvax®, a low dose of IMVAMUNE®, or a single high dose of IMVAMUNE® showed minimal to moderate clinical signs of the disease, but all survived the challenge. The only clinical sign displayed by rabbits that had been vaccinated twice with a high dose of IMVAMUNE® was mild transient anorexia in just two out of eight rabbits. This study shows that IMVAMUNE® can be a very effective vaccine against aerosolized RPXV.