Immunogenicity of a combined schedule of trivalent oral and inactivated polio vaccines in South African infants

Background : South Africa transitioned from using live-attenuated trivalent oral polio vaccine (tOPV), to a combination of tOPV and inactivated polio vaccine (IPV) in April 2009. We evaluated the immunogenicity of the South African combined tOPV-IPV schedule versus the tOPV-only schedule in South African infants. Methods : Serum samples of HIV-unexposed infants were analysed retrospectively from two cohorts; infants enrolled from April 2005 through June 2006 and infants enrolled from December 2009 to April 2010. The primary vaccination series of the tOPV-only schedule included doses at birth, 6, 10 and 14 weeks, and the tOPV-IPV schedule included tOPV at birth and 6 weeks and IPV at 6, 10 and 14 weeks. Serum polio neutralising antibody titres to serotype-1, serotype-2 and serotype-3 were evaluated in infants at 18 weeks of age. Results : Infants who received the tOPV-IPV schedule had higher GMTs than infants who received tOPV-only for serotype-2 (9.63 vs. 8.80, P < 0.001) and serotype-3 (10.01 vs. 8.53, P < 0.001), as well as higher sero-protective titres for serotype-1 (100% vs. 96%, P = 0.014). Conclusion : Our data support the option of the South African combined polio vaccination schedule as an immunogenic option for a combined schedule.