The performance of serological testing was strongly influenced by the duration of infection: sensitivity of IgM increased from 0.381 (95% CI: 0.300‐0.469) at Day 7 to 0.872 (95% CI: 0.784‐0.928) at Day 21, while sensitivity of IgG increased from 0.317 (95% CI: 0.200‐0.463) at Day 7 to 0.913 (95% CI: 0.823‐0.959) at Day 21. Here, CD40LG is linked to infection.