Protection against the poliovirus is lower at 1 month but remains sustained at 6 and 11 months after an inactivated poliovirus vaccine (IPV) boost following initial oral poliovirus vaccination (OPV), according to Jacob John, MD, of Christian Medical College, Vellore, Tamil Nadu, India, and his associates.

In a randomized controlled trial from Nov. 4 and Dec. 17, 2014, 900 healthy children from ages 1 to 4 years were randomly assigned between three study groups. The groups had the children receive IPV boost at 5 months (arm A), at enrollment (arm B), or no vaccine (arm C). Poliovirus shedding in stool 7 days after challenge, determined by Fisher’s exact test, was significantly lower in arms A and B, compared with C (risk ratio, 0.68; P = .003, RR, 0.70; P = .006 for arm A vs. C and B vs. C, respectively). The reduction in shedding was more marked for serotype 3 (RR, 0.60; P = .004, RR, 0.54; P = .001 respectively) than for serotype 1 (RR, 0.72; P = .057, RR, 0.80; P = .215, respectively).

Also, serum neutralizing antibody (NAb) titers were significantly higher 28 days after IPV in arms A and B, compared with 28 days after enrollment in control arm C (P values all less than .001). NAb titers diminished significantly by the time of Panacea Biotec (bOPV) challenge in all three arms (P values all less than .001 for each serotype in all three arms).

It was noted that 41 serious adverse events (11 in arm A, 17 in arm B, and 13 in arm C), including 2 deaths in arm A, were reported during the trial. However, the reported adverse events were classified as unrelated, and the deaths were from leukemia and from viral hemorrhagic fever.

“The boost to intestinal immunity against poliovirus that results from administration of IPV to OPV-vaccinated children is sustained at 6 and 11 months. It is clear that IPV is playing an increasingly important role in the polio endgame as the world transitions away from the use of OPV,” the researchers concluded. “Every effort needs to be made to ensure supply of this vaccine to meet this expanding role.”

Find the full study in the Journal of Infectious Diseases 2016. doi: 10.1093/infdis/jiw595 .