Effective Priming of Foals Born to Immune Dams against Influenza by a Canarypox-Vectored Recombinant Influenza H3N8 Vaccine

SummaryA classical limitation of early life immunization is the interference by maternally derived antibodies, which are known to inhibit the immune response to modified-live and killed vaccines. Several studies have convincingly shown that even minute amounts of maternally derived antibodies against equine influenza can strongly interfere with successful vaccination of foals born to immune mares. In this study we evaluated the response of foals born to vaccinated mares to immunization with a canarypox-vectored recombinant vaccine against equine influenza virus H3N8. The recombinant vaccine was able to efficiently prime foals in the presence of maternally derived immunity against influenza as was evidenced by a clear anamnestic antibody response when a secondary vaccination with the same vaccine was performed. The canarypox-vectored recombinant influenza vaccine therefore offers a unique opportunity to overcome the limitations of early life vaccination in the face of maternally derived immunity in foals.