In the pre-Py17x (−4 dpi) + CHIKV co-infection scenario, mice showed lower levels of CHIKV-specific IgM and IgG and reduced CHIKV neutralization compared to mice infected with CHIKV alone at both 6 and 15 dpi (Fig. 4d–f and Supplementary Fig. 6b). This evidence concerns the gene CD40LG and coinfection.