Maximising the impact of inactivated polio vaccines

With the globally coordinated switch from the trivalent oral polio vaccine (OPV) to the bivalent OPV in April, 2016, the international public health community entered a new chapter in the endgame of polio. Although OPV has served as the cornerstone of polio eradication efforts over the past 30 years, trivalent inactivated polio vaccine (IPV) has re-ascended to prominence in the past year, now acting as the sole source of protective immunity against type 2 poliovirus in routine immunisation programmes. Despite its immense public health value, the global supply of IPV is failing to meet demand. The October, 2016, meeting of the Strategic Advisory Group of Experts on Immunization cautioned that, “the IPV supply situation is further deteriorating; 50 countries are experiencing delays in supply or stock-outs, a situation which is likely to persist until 2018”. Given the existing resource constraints, pragmatic solutions are urgently needed to maximise the impact of IPVs during the transitional and post-OPV immunisation era. In The Lancet Infectious Diseases, Birgit Thierry-Carstensen and colleagues2 report one such novel strategy in the form of reduced-dose IPVs administered intramuscularly with an aluminium hydroxide (Al) adjuvant. The three IPV-Al candidates were formulated at one-third, one-fifth, and one-tenth the concentration of standard IPV and administered to healthy children living in the Dominican Republic at 6, 10, and 14 weeks of age. The results of the well conducted phase 2 trial indicate that the antigen-sparing IPV-Als were able to achieve substantial (ie, ≥75%) seroconversion against the three serotypes of polio after only two vaccine doses. Promisingly, after three doses, all three formulations of IPV-Als achieved more than 94% seroconversion to poliovirus types 1, 2, and 3, and the seroresponses were non-inferior to those of the standard IPV, which was administered unadjuvanted, but at up to ten-fold higher concentrations.