Background: As part of the global poliovirus eradication plan the use of live oral poliovirus vaccine (OPV) will soon be replaced with inactivated poliovirus vaccine (IPV) in order to eliminate any live virus which could continue to circulate and cause paralysis. The global transition from OPV to IPV must include evaluation of the impact of vaccination on intestinal poliovirus immunity, particularly in pediatric populations. However, adequate surrogate markers of intestinal immunity remain lacking. We report novel assays for measuring intestinal poliovirus antibody and OPV neutralization from fecal samples of children given both routine IPV as well as challenge doses of OPV.
Methods: Monthly stool samples from pediatric subjects were collected in Veracruz, Mexico in 2010-2011. Subjects had received at least 2 doses of IPV and were offered OPV twice yearly during national campaigns. OPV shedding was determined by real-time polymerase chain reaction. Thirty-six stool samples from 20 subjects were analyzed for total fecal immunoglobulin A (IgA) and IPV serotype 2 specific fecal IgA by means of enzyme-linked immunosorbent assays (ELISA), immunoblot (IB) and OPV serotype 2 neutralization assay.
Results: Total fecal IgA (n=36 samples) was detected from all samples tested. Nineteen of 36 samples analyzed by ELISA and 16 of 36 samples evaluated by IB had detectable IPV serotype 2 specific fecal IgA. The mean concentration of total fecal IgA was 55.2 mcg/ml and for IPV serotype 2 specific fecal IgA it was 0.016 mcg/ml. Statistical correlations were tested using χ² values. Neutralization titers correlated with both ELISA and IB assays of IPV serotype 2 specific fecal IgA (p=0.04 and p=0.02, respectively). There was a trend towards higher neutralization titers in those subjects who recently shed or were presently shedding OPV in stools but this did not reach significance (p=0.142).
Conclusion: Measurement of poliovirus specific fecal IgA is feasible, reproducible and correlates with OPV2 specific fecal neutralization assays. These assays, with further study, may provide a rapid and simple surrogate marker for intestinal immunity not only for poliovirus but for other enteric pathogens as well.
D. Bauer, None
C. Huang, None
J. Clements, None
Y. Maldonado, None