Figure 6
Two vaccinations with vIND-ZIKV are required to protect mice against ZIKV in mice with prior vector immunity. (a) Schematic of vaccination/challenge schedule and timing of blood collection in VACV-primed mice. Six-week-old immunocompetent C57BL/6 mice (n = 8) were vaccinated intramuscularly with PBS or 107 PFU vIND 2 weeks prior to first vaccination. Mice were then vaccinated with PBS or 107 PFU vIND or vIND-ZIKV (D4W) at weeks 0 and 2. Mice were challenged 2 weeks post-boost with 104 PFU ZIKV strain PRVABC59 intraperitoneally, 1 day after being administered 2 mg anti-IFNAR1 antibody intraperitoneally. (b) Anti-vector (VACV) antibodies were measured by ELISA in pooled serum collected at weeks − 2, 0, and 2. (c) ZIKV E-specific IgG titers were measured by ELISA at weeks 0, 2, 4 (1 day prior to challenge), and 6. (d) PRNTs were performed in twofold dilutions on pooled serum collected at the indicated time points. (e) ZIKV NS1-specific IgG titers were measured by ELISA at weeks 4 (1 day prior to challenge) and 6. (f) Viremia was measured in serum collected 2 days after ZIKV challenge by qRT-PCR. Asterisks represent statistical significance (*p < 0.05, †p < 0.005) by two-way repeated measures ANOVA (c,e) or unpaired t tests (f) compared to PBS-vaccinated control group. Horizonal lines represent geometric mean and error bars represent SD. LLD lower limit of detection.
