Fig. 2: Protection by ZPIV against homologous and heterologous ZIKV challenge during pregnancy.

Adult female C57BL/6 mice were i.m. immunized with two doses of either alum only (clear symbol) or ZPIV (solid symbol) as described in Fig. 1. After establishing pregnancy, the mice were challenged with either the ZK-PR strain or the ZK-BR strain at E9.5 and examined at 8 dpi (E17.5). a The percent protected dams carrying all fetuses with normal phenotype over the total number of dams. b The percent affected fetuses, based on gross fetal phenotype, of total fetuses. Gray regions indicate the fraction of phenotypically abnormal fetuses excluding those with complete fetal demise (solid black). The frequency of fetal demise in vaccinated mice was significantly reduced (P < 0.0001) using Fisher’s Exact test, compared with that of the group with alum alone. At 8 dpi, virus-neutralizing antibodies were determined as MN₅₀ titers (mean ± S.D.) in maternal serum samples (c) and fetal serum samples (d). Symbols represent individual mice challenged with ZK-PR (circle) or ZK-BR (square). The number of fetuses examined are open circles, n = 4; closed circles, n = 24; open squares, n = 3, closed squares, n = 27. The Kruskal-Wallis test was used for statistical analysis. The dotted line indicates the lowest serum dilution examined, which was 1:10 (c) and 1:400 (d). The percentage of fetal protection at 8 dpi was plotted against log10 MN₅₀ titers in maternal serum samples from alum only (clear circle, n = 13) and vaccinated (solid circle, n = 19) mice with combined groups challenged with ZK-PR or ZK-BR, as shown in Supplementary Table 3, at day −1 (e) and 8 dpi (f). The correlation was determined using the Spearman r-test. Spearman’s correlation coefficient, r = 0.8615 with 95% confidence interval (C.I.; dotted line), 0.733–0.931 in e and r = 0.7385 with the 95% C.I., 0.525–0.865 in f. The values were statistically significant, P < 0.0001.