Passive transfer of human sera from chikungunya virus virus-like particle vaccine (Vimkunya) recipients fully protects non-human primates from viremia

Vimkunya, a chikungunya virus (CHIKV) virus-like particle (VLP) vaccine, is well-tolerated and induces a rapid, durable serum neutralizing antibody (SNA) response in individuals aged ≥12 years. This study evaluated the efficacy of human CHIKV VLP antisera to protect cynomolgus macaques from heterologous CHIKV challenge and determined an SNA titer that confers complete protection against viremia. Macaques receiving negative control sera had detectable viremia and RNAemia, whereas those receiving control anti-CHIKV IgG or CHIKV VLP antisera with pre-challenge NT₈₀ ≥ 25.7 had no detectable viremia/RNAemia through 10 days post-challenge. Logistic regression showed that pre-challenge NT₈₀s of 23.6 and 25.9 corresponded with 80% and 90% probability of protection, respectively. Data from seroepidemiology studies demonstrated that a neutralizing titer of >1:10 is protective in convalescent persons. The SNA NT₈₀ threshold of 100 selected by US and European regulators to predict protection against CHIKV disease in humans is conservative by a factor of ~4.