We confirmed that Irf3/7−/− mice, infected with VLA1553 via the intraperitoneal route, developed readily detectable viraemia (Fig. 2C), with peak viraemia ~ 5.5–6.5 logs lower than those seen after infection of Irf3/7−/− mice with 4 log10CCID50 of CHIKV [43]. The gene discussed is IRF3; the disease is infection.