We suggest this week the article "Humoral and intestinal immunity induced by new schedules of bivalent oral poliovirus vaccine and one or two doses of inactivated poliovirus vaccine in Latin American infants: an open-label randomised controlled trial", recently published on The Lancet. 

AUTHORS: Edwin J Asturias, Ananda S Bandyopadhyay, Steve Self, Luis Rivera, Xavier Saez-Llorens, Eduardo Lopez, Mario Melgar, James T Gaensbauer, William C Weldon, M Steven Oberste, Bhavesh R Borate, Chris Gast, Ralf Clemens, Walter Orenstein, Miguel O'Ryan G, José Jimeno, Sue Ann Costa Clemens, Joel Ward, Ricardo Rüttimann

SUMMARY
Difficulties in the eradication of polio could be represented by the spread of wild polio virus internationally from the remaining endemic countries, or, on rare occasions, the reversion of live attenuated Sabin viruses from oral poliovirus vaccine (OPV) to neurovirulence. To eliminate type 2 vaccine-related disease, the Global Polio Eradication Initiative has recommended the global replacement of the trivalent oral poliovirus vaccine (tOPV) with bivalent types 1 and 3 oral poliovirus vaccine (bOPV) from April 2016, in addition to the inclusion of at least one dose of inactivated poliovirus vaccine (IPV) in primary immunisation series for all children worldwide. The authors reported the results of an observer-blinded, randomised, controlled, multicentre study. In this study, 940 Latin American infants were randomly assigned 1:1:1:1 to receive four different permutations of schedules: groups 1 and 2 received bOPV at 6, 10, and 14 weeks; group 3 received tOPV at 6, 10, and 14 weeks; group 4 received bOPV at 6, 10, and 14 weeks plus one dose of IPV at 14 weeks; and group 5 received bOPV at 6, 10, and 14 weeks plus two doses of IPV at 14 and 36 weeks. The authors highlighted as several important findings from this study are directly relevant to the polio endgame strategy. First, bOPV was at least as effective as tOPV in eliciting antibodies against types 1 and 3 in the EPI schedule, with both vaccines eliciting seroconversion rates above 95% after two doses; these findings support the switch from tOPV to bOPV in routine immunisation schedules. Second, one IPV dose in a bOPV primary series elicited type 2 seroconversion in 80.4% of infants, while more than half of those who had not seroconverted after IPV did so 1 week after oral type 2 exposure. The authors concluded that the prospective evaluation of humoral and intestinal immunity showed antibody responses after bOPV with one or two doses of IPV were non-inferior to those with tOPV or bOPV-only schedules for serotypes 1 and 3, and were superior to bOPV-only schedules for serotype 2. More than 90% of bOPV vaccines seroconverted or were primed to type 2 by one dose of IPV. IPV also induced small but statistically significant increases in intestinal immunity to type 2, compared with bOPV alone, suggesting some enhancement of intestinal protection. As the world prepares to move to routine bOPV–IPV immunisation schedules during 2016–2019, with monovalent type 2 vaccine (mOPV2) intended for outbreak response, the authors hope that this study serves as a surrogate of future vaccination strategies and provides important evidence for the formulation of national, regional, and global policies in this final, historic phase of polio eradication.

To learn more, go to the full article.