Anti-tetravalent VLP sera protective assay in suckling mice. Protective effects of mouse antisera from the tetravalent VLP group were evaluated in suckling mice. Mice were intracerebrally inoculated with DENV1, 2, 3 or 4 and clinical signs of infection, mainly hind leg paralysis, alterations in spinal column and mortality, were monitored for 21 days. (A) survival curve; (B) mobidity curve. Different letters mean statistically significant differences by the Log-rank test. *indicates statistical significance (*P < 0.05; ** P < 0.01).