Antibody levels against polioviruses in children following pulse polio immunization program

This cross sectional study was performed in a tertiary level teaching hospital to evaluate and compare the antibody levels in children below 6 years who had received oral polio vaccination through Pulse Polio Immunization (PPI) with those children who had received both routine immunization as well as PPI. Detail history of polio immunization was taken. Serum samples were then collected for antibody determination by neutralization tests with standard polio viruses using Vero cell lines. Total 400 children were studied; 14 were found unvaccinated. Out of the remaining 386 (96.5%) vaccinated children, 292 (75%) had received both routine and pulse polio immunization, 68 (17%) had only PPI while 26 (6.7%) had received only routine immunization. The seropositivity was lowest for P3 and highest for P2. Overall seroprevalence for P1, P2 and P3 in vaccinated children was 89.1%, 93% and 80.6% respectively, and did not differ significantly between the three vaccinated subgroups. However, children who were immunized by both routine and PPI had higher geometric mean titers (315.5, 484.7 and 187.4 for P1, P2 and P3 respectively) when compared with those who had received only PPI (P<0.001 for each P1, P2 and P3), as well as those who had received only routine immunization with OPV (P<0.05 for P1, p<0.001 for P2, and P<0.01 for P3). Despite the reasonable immunization coverage in study population, there were 29 (7.25%) triple negative cases. Hence other causes of low seroconversion should also be considered to achieve polio free India.