A novel Pan-viral prophylaxis strategy using vaccine adjuvant CAF09b protects against influenza virus infection

The SARS-CoV-2 pandemic caused a massive health and societal crisis, although the fast development of effective vaccines reduced some of the impact. To prepare for future pandemics, a pan-viral prophylaxis could be used to control the initial virus outbreak in the period prior to vaccine approval. The liposomal vaccine adjuvant CAF(R)09b contains the TLR3 agonist polyinosinic:polycytidylic acid, which induces a type I interferon (IFN-I) response and an antiviral state in the affected tissues. When testing CAF09b as a potential pan-viral prophylaxis, we observed that intranasal administration of CAF09b to mice resulted in an influx of innate immune cells into the nose and lungs and upregulation of IFN-I related gene expression. When CAF09b was administered prior to challenge with mouse-adapted influenza A/Puerto Rico/8/1934 virus, it protected from severe disease, although virus was still detectable in the lungs. However, when CAF09b was administered after influenza challenge, the mice had a similar disease course to controls. In conclusion, CAF09b may be a suitable candidate as a pan-viral prophylactic treatment for epidemic viruses, but must be administered prior to virus exposure to be effective.