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

Abstract

SummaryBackgroundPakistan and Afghanistan are two of the three remaining countries yet to interrupt wild-type poliovirus transmission. The increasing incidence of poliomyelitis in these countries during 2010–11 led the Executive Board of WHO in January, 2012, to declare polio eradication a “programmatic emergency for global public health”. We aimed to establish why incidence is rising in these countries despite programme innovations including the introduction of new vaccines.MethodsWe did a matched case-control analysis based on a database of 46 977 children aged 0–14 years with onset of acute flaccid paralysis between Jan 1, 2001, and Dec 31, 2011. The vaccination history of children with poliomyelitis was compared with that of children with acute flaccid paralysis due to other causes to estimate the clinical effectiveness of oral poliovirus vaccines (OPVs) in Afghanistan and Pakistan by conditional logistic regression. We estimated vaccine coverage and serotype-specific vaccine-induced population immunity in children aged 0–2 years and assessed their association with the incidence of poliomyelitis over time in seven regions of Afghanistan and Pakistan.FindingsBetween Jan 1, 2001, and Dec 31, 2011, there were 883 cases of serotype 1 poliomyelitis (710 in Pakistan and 173 in Afghanistan) and 272 cases of poliomyelitis serotype 3 (216 in Pakistan and 56 in Afghanistan). The estimated clinical effectiveness of a dose of trivalent OPV against serotype 1 poliomyelitis was 12·5% (95% CI 5·6–18·8) compared with 34·5% (16·1–48·9) for monovalent OPV (p=0·007) and 23·4% (10·4–34·6) for bivalent OPV (p=0·067). Bivalent OPV was non-inferior compared with monovalent OPV (p=0·21). Vaccination coverage decreased during 2006–11 in the Federally Administered Tribal Areas (FATA), Balochistan, and Khyber Pakhtunkhwa in Pakistan and in southern Afghanistan. Although partially mitigated by the use of more effective vaccines, these decreases in coverage resulted in lower vaccine-induced population immunity to poliovirus serotype 1 in FATA and Balochistan and associated increases in the incidence of poliomyelitis.InterpretationThe 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.FundingPoliovirus Research subcommittee of WHO, Royal Society, and Medical Research Council.

The effect of azithromycin on the immunogenicity of oral poliovirus vaccine: a double-blind randomised placebo-controlled trial in seronegative Indian infants

“…In the case of oral poliovirus vaccine (OPV), impaired efficacy of the vaccine has stalled eradication and required the use of frequent, often monthly mass vaccination campaigns in endemic regions. 3,4 The biological mechanisms underlying poor oral vaccine performance in low-income countries have not been elucidated, although several candidates have been proposed. Some may be common to a number of oral vaccines, such as interference with the immune response in infants by high-levels of homologous maternal antibodies transferred via the placenta or breast-feeding.…”

Polio Vaccines: Present and Future

“…Например, в некоторых штатах Северной Индии показатель сероконверсии после введения дозы вакцины составлял менее 10%. Это требовало до-полнительной вакцинации для достижения уровня иммунизации населения в 85-90%, необходимого для остановки распространения вируса [67][68][69][70]. При таком низком уровне иммуногенности для иммунизации большинства детей было необходи-мо ввести каждому более 15 доз вакцин, на что требовалось около 2-х лет.…”

Current Status and Future of Polio Vaccines and Vaccination

“…For instance, in some states in northern India the per-dose seroconversion rate was found to be less than 10 %, requiring multiple repeated vaccinations to reach the population immunity level of 85-90 % needed to stop virus transmission (Patriarca et al 1991;Grassly et al 2006Grassly et al , 2007O'Reilly et al 2012). At this low level of immunogenicity, more than 15 doses of vaccine were needed to immunize most children, which takes up to 2 years.…”

“…In addition, wild type 2 poliovirus was eradicated in 1999, and therefore maintaining high immunity against type 2 poliovirus was a lower priority than stopping transmission of types 1 and 3. Introduction of monovalent OPV1 and OPV3 and then bivalent OPV1 + 3 vaccine succeeded, and the circulation of wild polioviruses in India was interrupted in 2011 (John and Vashishtha 2012;Kaura and Biswas 2012;O'Reilly et al 2012).…”