Comparison of neutralization titers for human sera obtained by PRNT or RVPs.

NT50 neutralization titers for sera were obtained using DENV RVPs or conventional PRNT with live virus and are expressed as reciprocal serum dilutions at which viral infection was inhibited by 50%. All reference sera were obtained from the National Institute of Biological Standards and Controls (NIBSC). RVPa and RVPb values were obtained from independent experiments performed in different laboratories (IM and UCB) and were compared to PRNT values obtained in an independent study conducted by the WHO for validation testing of PRNT for DENV clinical studies [23]. All sera were tested at least three times. Mean NT50 values using PRNT and RVPs were not statistically different (ANOVA, p>0.05). ‘<10’ (non-neutralizing) indicates a calculated NT50 value of <10 or the failure of the sera to neutralize by at least 50%. NT50 values <10 were calculated as 10.0 for statistical analysis. ND = not determined.