Gap in the prevalence of neutralising antibodies to polioviruses in antenatal women in southern India.

With the disappearance of circulating wild poliovirus and improved sanitation, protective antibody levels may wane over time following oral poliovirus vaccine (OPV) administration. This study evaluated the seroprevalence of neutralising antibodies to vaccine polioviruses among young Indian women who had received at least three doses of OPV as primary immunisation. Of 60 women studied, 27 (45%) had antibody titres of <1:8 to one or more polioviruses, with the lowest levels for poliovirus types 3 and 1. These findings represent a possible immunity gap and this needs to be confirmed with further studies, which could include a challenge with vaccine virus.

Circulating vaccine derived polio viruses and their impact on global polio eradication.

Poliomyelitis vaccination via live Oral Polio Vaccine (OPV) suffers from the inherent problem of reversion: the vaccine may, upon replication in the human gut, mutate back to virulence and transmissibility resulting in circulating vaccine derived polio viruses (cVDPVs). We formulate a general mathematical model to assess the impact of cVDPVs on prospects for polio eradication. We find that for OPV coverage levels below a certain threshold, cVDPVs have a small impact in comparison to the expected endemic level of the disease in the absence of reversion. Above this threshold, the model predicts a small but significant endemic level of the disease, even where standard models predict eradication. In light of this, we consider and analyze three alternative eradication strategies involving a transition from continuous OPV vaccination to either continuous Inactivated Polio Vaccine (IPV), pulsed OPV vaccination, or a one-time IPV pulse vaccination. Stochastic modeling shows continuous IPV vaccination is effective at achieving eradication for moderate coverage levels, while pulsed OPV is effective if higher coverage levels are maintained. The one-time pulse IPV method may also be a viable strategy, especially in terms of the number of vaccinations required and time to eradication, provided that a sufficiently large pulse is practically feasible. More investigation is needed regarding the frequency of revertant virus infection resulting directly from vaccination, the ability of IPV to induce gut immunity, and the potential role of spatial transmission dynamics in eradication efforts.

Effect of vitamin A administered at Expanded Program on Immunization contacts on antibody response to oral polio vaccine.

OBJECTIVE: Vitamin A supplementation to mothers in the postpartum period and to their infants at routine immunization contacts is being considered to reduce vitamin A deficiency in infancy. This study was conducted to determine the impact of maternal and infant vitamin A supplementation on antibody response to oral polio vaccine (OPV). DESIGN: Randomized, double blind, placebo-controlled trial. INTERVENTIONS: Mothers in the intervention group received 60 mg retinol equivalent (RE) vitamin A 3-4 weeks after delivery and their infants 7.5 mg RE with each OPV dose at 6, 10 and 14 weeks of age. The control group mothers and their infants received a placebo at each of these contacts. MAIN OUTCOMES: Geometric mean (GM) titer of neutralizing antibodies and proportion of children with protective titer to the three polioviruses at 26 weeks of age. RESULTS: Vitamin A supplementation increased the proportion of infants with protective antibody titer against poliovirus type 1 (relative risk (RR) 1.15, 95% confidence interval (CI) 1.03-1.28) and the GM antibody titer (ratio of GM 1.55, 95% CI 1.03-2.31) following immunization. The proportion of infants with protective antibody titer against poliovirus type 2 (RR 0.99, 95% CI 0.94-1.05) or type 3 (RR 1.05, 95% CI 0.96-1.15) was not significantly different in vitamin A and placebo groups. The GM antibody titer for poliovirus type 2 (ratio of GM 0.99, 95% CI 0.64-1.54) or poliovirus type 3 (ratio of GM 1.10, 95% CI 0.69-1.75) also did not differ across groups. CONCLUSIONS: Vitamin A given to the mothers in the postpartum period and their infants with OPV did not interfere with the antibody response to any of the three polioviruses and enhanced the response to poliovirus type 1.