Abstract
In 2014, inactivated poliovirus vaccine (IPV) campaigns were implemented in Nigeria and Pakistan after clinical trials showed that IPV boosts intestinal immunity in children previously given oral poliovirus vaccine (OPV). We estimated the effect of these campaigns by using surveillance data collected during January 2014–April 2016. In Nigeria, campaigns with IPV and trivalent OPV (tOPV) substantially reduced the incidence of poliomyelitis caused by circulating serotype-2 vaccine–derived poliovirus (incidence rate ratio [IRR] 0.17 for 90 days after vs. 90 days before campaigns, 95% CI 0.04–0.78) and the prevalence of virus in environmental samples (prevalence ratio [PR] 0.16, 95% CI 0.02–1.33). Campaigns with tOPV alone resulted in similar reductions (IRR 0.59, 95% CI 0.18–1.97; PR 0.45, 95% CI 0.21–0.95). In Pakistan, the effect of IPV+tOPV campaigns on wild-type poliovirus was not significant. Results suggest that administration of IPV alongside OPV can decrease poliovirus transmission if high vaccine coverage is achieved.
Highlights
The live attenuated oral poliovirus vaccine (OPV) is cheap and easy to administer; it has been the vaccine of choice for the Global Polio Eradication Initiative
The prevalence of circulating VDPV serotype 2 (cVDPV2) was reduced among environmental samples collected in the same districts as the campaigns; this reduction was not statistically significant (PR 0.16 based on the mixed-effects regression, 95% CI 0.02–1.33; p = 0.09)
Campaigns with trivalent OPV (tOPV) alone did not significantly reduce the incidence of poliomyelitis associated with cVDPV2 (IRR 0.59, 95% CI 0.18–1.97; p = 0.215 for comparison with inactivated poliovirus vaccine (IPV)+tOPV campaigns), but they did significantly reduce the prevalence of cVDPV2 in the environment (PR 0.45, 95% CI 0.21–0.95; p = 0.369 for comparison with IPV+tOPV campaigns)
Summary
The live attenuated oral poliovirus vaccine (OPV) is cheap and easy to administer; it has been the vaccine of choice for the Global Polio Eradication Initiative. This boost was greater than that observed after an additional dose of OPV These encouraging findings motivated the introduction, beginning in 2014, of IPV to mass vaccination campaigns in Nigeria and Pakistan, 2 countries that had circulating VDPV and wild-type poliovirus at that time. It is not yet known whether the IPV boost of intestinal immunity observed against a challenge dose of vaccine (Sabin) poliovirus will translate to an effect of IPV campaigns on transmission of wild-type polioviruses and VDPVs at the community level. We report the results of that analysis and discuss their implications for the polio endgame strategy
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