ANTIBODY-RESPONSE AND VIRAL EXCRETION AFTER LIVE POLIO VACCINE OR A COMBINED SCHEDULE OF LIVE AND INACTIVATED POLIO VACCINES

A randomized controlled trial was performed in infants undergoing rout ine immunization in North Hertfordshire. Ninety six children received a single dose of inactivated polio vaccine, followed by two doses of l ive attenuated oral polio vaccine and 97 children received three doses of live attenuated oral polio vaccine at 2, 3 and 4 months of age. Bl ood samples were taken by study nurses 6 weeks after vaccination and s tool samples were collected by parents weekly for 4 weeks after each d ose of vaccine. Follow-up was completed for 92 of 96 (96%) children in the combined schedule group and 92 of 97 (95%) in the control group. After vaccination the proportions of children with detectable antibody to poliovirus serotypes 1, 2 and 3 were high and similar between grou ps and geometric mean titers (95% confidence interval) to poliovirus t ypes 1, 2 and 3 were 264 (200 to 347), 375 (311 to 450) and 189 (144 t o 250) in the combined schedule group and 369 (290 to 469), 401 (321 t o 498) and 206 (145 to 293) in the live vaccine group, respectively. T he only significant difference between groups in rates of viral excret ion was observed after the second dose of live attenuated oral polio v accine, when excretion of type 3 poliovirus was reduced in those child ren who had received prior inactivated polio vaccine (P = 0.05). This study suggests that, com pared with the current schedule, a combined s chedule of inactivated and live poliovaccines is likely to produce equ ivalent individual protection against poliomyelitis and is unlikely to substantially alter circulation of poliovirus in the community. Becau se the risk of vaccine-associated poliomyelitis is greatest after the first dose of poliovaccine, this schedule could also reduce the risk t o vaccine recipients.