doi:10.1038/nindia.2014.114 Published online 22 August 2014
A single injection of inactivated poliovirus vaccine (IPV) could boost the immunity of children already vaccinated with multiple doses of live oral poliovirus vaccine (OPV), new research suggests1.
A combination of the two vaccine types in routine immunisation programmes could help achieve global eradication of poliovirus, the researchers say.OPVs are cheaper and easier to administer but the intestinal immunity they provide against the virus weakens after a while. Children vaccinated with OPV can still spread the virus through faeces.
An international team of researchers has now tested the efficacy of IPV in boosting intestinal immunity of OPV-vaccinated children. In clinical trials conducted in the Moradabad district of Uttar Pradesh, they tested stool samples of nearly a thousand infants and children vaccinated multiple times with OPV. The children were divided into random groups and given either bivalent OPV (bOPV), containing type 1 and type 3 polioviruses, or IPV. A third group (the control) was not given any vaccine.
The groups were challenged with a dose of live but weakened polioviruses type 1 and 3 to test their intestinal immunity 28 days later. “When we gave the challenge dose to people who did not have immunity, the virus multiplied in the gut and got shed in the stools,” explains Sunil Bahl, Deputy Project Manager of WHO’s India-National Polio Surveillance Project and co-author of the study. The trials showed that IPV boosted intestinal immunity among OPV-vaccinated children better than an additional dose of OPV.
Those who received IPV showed considerable reduction in shedding of poliovirus type 1 (39–74%) and type 3 (53–76%) across different age groups as compared to the control group. On the other hand, bOPV showed a 52% reduction of type 1 and 40.5% reduction of type 3 poliovirus excretion only in 10-year-olds. Its effect on infants and 5-year-olds was found to be negligible compared to control.
The results of the study have already borne fruit. Its preliminary data has guided the development of the Polio Eradication and Endgame Strategic Plan (2013–2018), says Roland Sutter, lead author of the study who coordinates polio research and product development at WHO, Geneva. According to the plan, at least one dose of IPV has to be introduced in routine immunisations. So far, 70 countries have integrated it and an almost equal number has expressed interest in doing so, Sutter said. Though India has been declared polio-free, the government plans to roll out IPVs in 2015 to prevent polio resurgence.
Jacob John, Professor in community medicine at Christian Medical College in Vellore, who published similar findings2 last month, said both studies show that children primed with oral vaccines get a substantial immunity boost from IPV, “protecting against excretion of poliovirus” and its spread. “The implications are that IPVs can be used by the (polio) eradication initiative in mass campaigns to boost immunity and speed up elimination in the remaining infected areas, and as a booster for travelers to prevent spread of infection,” John told Nature India.