Polio vaccination in Pakistan

Abstract

Transmission of wild poliovirus (WPV) types 1 and 3 continued in Pakistan in 2012 (Aug 4, p 491).1O'Reilly KM Durry E Islam O et al.The effect of mass immunisation campaigns and new oral poliovirus vaccines on the incidence of poliomyelitis in Pakistan and Afghanistan, 2001–11: a retrospective analysis.Lancet. 2012; 378: 491-498Summary Full Text Full Text PDF Scopus (46) Google Scholar The per-dose vaccine efficacy of trivalent oral polio vaccine (OPV) against WPV-1 was estimated to be only 12·5%.1O'Reilly KM Durry E Islam O et al.The effect of mass immunisation campaigns and new oral poliovirus vaccines on the incidence of poliomyelitis in Pakistan and Afghanistan, 2001–11: a retrospective analysis.Lancet. 2012; 378: 491-498Summary Full Text Full Text PDF Scopus (46) Google Scholar Even 100% coverage with a realistic number of trivalent OPV doses cannot eliminate WPV-1 where vaccine efficacy is so low. O'Reilly and colleagues recommend bivalent OPV for supplementary immunisation activities in preference to monovalent OPV-1 for the added advantage of addressing WPV-3 but without losing the edge on WPV-1. However, this logic is correct only for one dose; when additional doses are given, the build-up of vaccine efficacy is faster for monovalent OPV than for bivalent OPV. The cumulative vaccine efficacy with additional doses is determined by the per-dose efficacy.2John TJ Immunisation against polioviruses in developing countries.Rev Med Virol. 1993; 3: 149-160Crossref Scopus (31) Google Scholar The efficacy of two doses (E2) can be calculated by the formula E1 + (E1[100 – E1]), where E1 is the per-dose efficacy. The efficacy of three doses, E3, is E2 + (E1[100 – E2]). In this way we have calculated the cumulative efficacies of the three vaccines for up to six doses (table). The vaccine efficacy achievable with two doses of monovalent OPV-1 matches that of three doses of bivalent OPV; the vaccine efficacy of three doses of monovalent OPV-1 matches that of five doses of bivalent OPV.TableCumulative efficacies of the three oral polio vaccines (OPVs) against wild poliovirus type 1Dose 1Dose 2Dose 3Dose 4Dose 5Dose 6Trivalent OPV12·5%23·4%33·0%41·4%48·7%55·1%Bivalent OPV23·4%41·3%55·0%65·5%73·5%79·7%Monovalent OPV34·5%57·1%71·9%81·6%88·9%92·7% Open table in a new tab With the use of monovalent OPV-1 for supplementary immunisation activities, WPV-1 elimination ought to be targeted first; after achieving this, bivalent OPV should be substituted to eliminate WPV-3 while keeping WPV-1 under check. This stratagem was successfully applied in northern India.3Grassly NB Wenger J Durrani S et al.Protective efficacy of a monovalent oral type 1 poliovaccine: a case-control study.Lancet. 2007; 369: 1356-1362Summary Full Text Full Text PDF PubMed Scopus (132) Google Scholar Simultaneously addressing WPV-1 and WPV-3 now in Pakistan could be a tactical error which might delay the interruption of WPV-1, allow its resurgence, and delay polio eradication globally. We declare that we have no conflicts of interest. The effect of mass immunisation campaigns and new oral poliovirus vaccines on the incidence of poliomyelitis in Pakistan and Afghanistan, 2001–11: a retrospective analysisThe effectiveness of bivalent OPV is comparable with monovalent OPV and can therefore be used in eradicating serotype 1 poliomyelitis whilst minimising the risks of serotype 3 outbreaks. However, decreases in vaccination coverage in parts of Pakistan and southern Afghanistan have severely limited the effect of this vaccine. Full-Text PDF Open AccessPolio vaccination in Pakistan – Author's replyWe agree with Jacob John and Vipin Vashishtha that achieving high population immunity is essential in Pakistan and Afghanistan if elimination of poliomyelitis is to be achieved. Full-Text PDF