RBP4 and COVID-19: RBP4 was associated with COVID-19 susceptibility using the Wald ratio (OR: 0.83, 95% CI: 0.72–0.95, P: 0.0072) at a significance threshold (P < 5 × 10− 8), but the association was not significant (OR: 0.96, 95% CI: 0.91–1.02, P: 0.2693) at a liberal significance threshold (P < 5 × 10− 6).