Longitudinal dynamics and lineage cross-reactivity of the human antibody response to West Nile virus

West Nile virus (WNV) is an emerging/re-emerging flavivirus representing one of the major global causes of mosquito-borne encephalitis, yet no approved therapeutics or vaccines currently exist. To characterize the kinetics of WNV-specific immunity, we evaluated the humoral response in a longitudinal cohort of 55 WNV lineage 1-infected blood donors up to 1 year. We demonstrate that WNV infection elicits robust and durable binding and neutralizing antibodies. Using a biphasic decay model, we estimated the half-life of neutralizing antibodies to be 37 days during the rapid decay phase and 472 days during the extended slow decay phase. Notably, the magnitude and durability of these antibodies were largely independent of viral RNA persistence in the whole blood (WB) compartment. To assess the breadth of this response, we evaluated cross-reactivity against an emerging divergent WNV lineage 2 strain and observed that WNV lineage 1-immune sera exhibited reduced neutralizing activity with high variability between donors during both acute and convalescent phases. These deficits in heterologous neutralization were reciprocally confirmed using an independent WNV cohort from Italy. Together, our results establish that lineage-specific divergence results in antibodies with a highly variable reduction in neutralization, indicating that successful WNV vaccine candidates should overcome this variability to confer pan-lineage protection.IMPORTANCEWest Nile virus (WNV) is a growing global health threat spread by mosquitoes that can cause severe disease, yet there are currently no approved vaccines or treatments available. We followed 55 WNV lineage 1-infected blood donors up to 1 year to study their antibody response to infection. We found that natural infection generates a long-lasting antibody response. Interestingly, the magnitude and durability of these antibodies were maintained regardless of viral RNA persistence in the whole blood compartment. However, a potential gap in cross-protective immunity emerged when we examined WNV lineage 1-specific antibodies against WNV lineage 2, a genetically distinct and divergent viral strain with over 25 mutations in the envelope protein. Sera from WNV lineage 1-infected donors showed a highly variable reduction in neutralizing activity against lineage 2 WNV during both the acute and convalescent phases of infection. We corroborated this observation using an independent cohort of patients from Italy, again demonstrating reduced cross-neutralization between the two viral lineages. Together, our results establish that lineage-specific divergence results in reduced cross-neutralization of heterologous strains, indicating that successful WNV vaccine candidates should overcome this barrier to confer pan-lineage protection.