Figure 4. MVA-CHIK candidate vaccine fully protects BALB/c mice against CHIKV viremia.

BALB/c mice were vaccinated with a prime and boost (day 28) of 10⁷ TCID₅₀ units of MVA-CHIK vaccine virus and then challenged with 10⁴ TCID₅₀ units of wild-type CHIKV intradermally (in the hind left footpad) two weeks post-boost. Prior to challenge, BALB/c mice were bled and serum was monitored for neutralizing activity by TCID₅₀ micro-neutralization assay (A). Mice were bled two days following challenge and viremia levels were measured via TCID₅₀ (B). For passive immunization, prime and boost vaccinated BALB/c and A129 mice were bled and serum taken from each mouse was pooled with equal volumes into separate pools from each strain. Pools of serum (100 µL for BALB/c and 200 µL for A129) were then injected i.p. into A129 mice which were challenged 24 hrs later with 10² TCID₅₀ units of wild-type CHIKV. Viremia was measured 2 d.p.i (C) and survival was monitored for two weeks post-challenge (D). The dotted line indicates the limit of detection of the assay.