Immunogenicity to poliovirus type 2 following two doses of fractional intradermal inactivated poliovirus vaccine: A novel dose sparing immunization schedule

Introduction: The polio eradication endgame strategic plan calls for the sequential removal of Sabin polio virus serotypes from the trivalent oral poliovirus vaccine (tOPV), starting with type 2, and the introduction of >= I dose of inactivated poliovirus vaccine (IPV), to maintain an immunity base against poliovirus type 2. The global removal of oral poliovirus type 2 was successfully implemented in May 2016. However, IPV supply constraints has prevented introduction in 21 countries and led to complete stock-out in >20 countries. Methods: We conducted a literature review and contacted corresponding authors of recent studies with fractional-dose IPV (flPV), one-fifth of intramuscular dose administered intradermally, to conduct additional type 2 immunogenicity analyses of two flPV doses compared with one full-dose IPV. Results: Four studies were identified that assessed immunogenicity of two flPV doses compared to one full-dose IPV. Two fractional doses are more immunogenic than 1 full-dose, with type 2 seroconversion rates improving between absolute 19-42% (median: 37%, p < 0.001) and relative increase of 53-125% (median: 82%), and antibody titer to type 2 increasing by 2-32-fold (median: 10-fold). Early age of administration and shorter intervals between doses were associated with lower immunogenicity. Discussion: Overall, two flPV doses are more immunogenic than a single full-dose, associated with significantly increased seroconversion rates and antibody titers. Two flPV doses together use two-fifth of the vaccine compared to one full-dose IPV. In response to the current IPV shortage, a schedule of two flPV doses at ages 6 and 14 weeks has been endorsed by technical oversight committees and has been introduced in some affected countries. (C) 2017 Published by Elsevier Ltd.