Extra Inactivated Polio Vaccine Dose Boosts Immunity

Ricki Lewis, PhD

July 11, 2014

Children given inactivated polio vaccine (IPV) at least 6 months after the oral poliovirus vaccine (OPV) series develop better immunity, according to a report published online July 11 in the Lancet.

Polio remains endemic in Pakistan, Afghanistan, and Nigeria. A contributing factor to the persistence of this illness is the waning of intestinal mucosal immunity a year after OPV. This report shows that adults who had OPV as children and who were given immunoglobulin A develop more robust cellular and humoral immunity, suggesting OPV can prime the injected vaccine.

Jacob John, MD, from Christian Medical College, Vellore, Tamil Nadu, India, and colleagues hypothesize that administering IPV containing serotypes 1, 2, and 3 to children already immunized with OPV might strengthen the intestinal immune response. In an open-label, randomized controlled trial, the researchers assigned 450 healthy children aged 1 to 4 years from Vellore, India, who had not received IPV before and who had had the most recent of at least 5 doses of OPV within 6 months to either receive IPV or not.

The researchers assessed immune response as the proportion of children shedding poliovirus 7 days after a challenge dose of bivalent OPV. A second dose of OPV given to children in the no-vaccine group enabled the researchers to assess intestinal immunity in response to the first dose.

Adding IPV increased serum antibody response to poliovirus challenge. A week after the OPV challenge, 224 children in the IPV group and 222 children in the no-vaccine group had provided stool samples. In the IPV group, 27 (12%) of the children shed serotype 1 poliovirus and 17 (8%) shed serotype 3 poliovirus compared with 43 (19%) and 57 (26%) in the no-vaccine group (risk ratio, 0.62 [95% confidence interval, 0.40 - 0.97; P = .0375] and 0.30 [95% confidence interval, 0.18 - 0.49; P < .0001], respectively).

Among children in the no-vaccine group, the first dose of bivalent OPV did not reduce poliovirus shedding after a second challenge dose.

Adding IPV, especially after the planned 2016 global withdrawal of serotype 2 OPV, could reduce transmission by travelers, boost protection in endemic areas, and maximize herd immunity, the researchers conclude.

A limitation of the study was the use of attenuated poliovirus in the challenges, which would not elicit as strong an immune response as exposure to wild poliovirus.

In an accompanying comment, Kimberly Thompson, ScD, from the University of Central Florida College of Medicine, reviews global efforts to eradicate all 3 poliovirus serotypes, pointing out cases since 2000 of imported wild polioviruses. The current study provides an important model for extrapolating from individual to population immunity, she writes. "However, the effects on overall population immunity and cost-effectiveness of an extra dose remain uncertain, and comparisons between extra IPV and OPV doses on population immunity must account for their differences in seroconversion, secondary spread, and cost."

The Bill and Melinda Gates Foundation funded the study. The authors and commentator have disclosed no relevant financial relationships.

Lancet. Published online July 11, 2014. Article abstract, Comment extract

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