Multivariate logistic regression models assessed independent and interactive predictors of symptomatic and severe disease, and ROC curve analysis was performed to quantify their discriminative ability.<h4>Results</h4>An interaction between the absence of both the protective tAB1/wL KIR motif and the Neanderthal-derived OAS1/2/3 alleles significantly predicted symptomatic infection (OR 3.47, P = 0.006) and severe disease (OR 2.41, P = 0.038), achieving overall classification accuracies of 75.4% and 78.9%, respectively. The gene discussed is OAS1; the disease is infection.