Incidence Of Poliomyelitis Research Articles

Molecular Epidemiology of Wild Poliovirus Type 1 and Shift in the Historically Reservoir Areas of Pakistan During 2019-2022.

Pakistan is one of the two countries endemic for wild poliovirus type 1 (WPV1). Active clinical and environmental wastewater surveillance along with laboratory investigation is an integral and primary component of the polio eradication strategies. The current study is mainly focused on the virological data to understand the current epidemiology of WPV1 in Pakistan during 2019-2022. 141,037 stool specimens of patients reported with acute flaccid paralysis (AFP) and 3,171 wastewater samples were tested for poliovirus detection using cell culture and PCR. Phylogenetic analysis of WPV1 was performed using MEGA and Nextstrain. Poliovirus isolates were classified into 15 distinct genetic clusters with multiple transmission lineages. Spatio-temporal trends indicated a significant decline in the incidence of poliomyelitis reported in 58 districts in 2019 to just 3 in 2022. The historical reservoirs in Peshawar, Quetta, and Karachi successfully eliminated the indigenous transmission chains of wild poliovirus active there for years. Our findings reinforce the evolving epidemiology of poliovirus in Pakistan which is now confined to South KP. All historically known reservoirs in Peshawar, Karachi and Quetta blocs are now free of poliovirus. Intensified clinical and environmental surveillance should be maintained to eliminate the very few remaining transmission lineages and certify the poliovirus eradication by 2026.

Potential Future Use, Costs, and Value of Poliovirus Vaccines.

Countries face different poliovirus risks, which imply different benefits associated with continued and future use of oral poliovirus vaccine (OPV) and/or inactivated poliovirus vaccine (IPV). With the Global Polio Eradication Initiative (GPEI) continuing to extend its timeline for ending the transmission of all wild polioviruses and to introduce new poliovirus vaccines, the polio vaccine supply chain continues to expand in complexity. The increased complexity leads to significant uncertainty about supply and costs. Notably, the strategy of phased OPV cessation of all three serotypes to stop all future incidence of poliomyelitis depends on successfully stopping the transmission of all wild polioviruses. Countries also face challenges associated with responding to any outbreaks that occur after OPV cessation, because stopping transmission of such outbreaks requires reintroducing the use of the stopped OPV in most countries. National immunization program leaders will likely consider differences in their risks and willingness‐to‐pay for risk reduction as they evaluate their investments in current and future polio vaccination. Information about the costs and benefits of future poliovirus vaccines, and discussion of the complex situation that currently exists, should prove useful to national, regional, and global decisionmakers and support health economic modeling. Delays in achieving polio eradication combined with increasing costs of poliovirus vaccines continue to increase financial risks for the GPEI.

A possible role for B cells in COVID-19? Lesson from patients with agammaglobulinemia

Summary COVID-19 had a mild clinical course in patients with Agammaglobulinemia lacking B lymphocytes, whereas it developed aggressively in Common Variable Immune Deficiency. Our data offer mechanisms for possible therapeutic targets.

Neutralization capacity of highly divergent type 2 vaccine-derived polioviruses from immunodeficient patients

The use of the oral poliovirus vaccine (OPV) in developing countries has reduced the incidence of poliomyelitis by >99% since 1988 and is the primary tool for global polio eradication. Spontaneous reversions of the vaccine virus to a neurovirulent form can impede this effort. In persons with primary B-cell immunodeficiencies, exposure to OPV can result in chronic infection, mutation, and excretion of immunodeficiency-associated vaccine-derived polioviruses, (iVDPVs). These iVDPVs may have the potential for transmission in a susceptible population and cause paralysis. The extent to which sera from OPV recipients are able to neutralize iVDPVs with varying degrees of antigenic site substitutions is investigated here. We tested sera from a population immunized with a combination vaccine schedule (both OPV and inactivated polio vaccine) against a panel of iVDPVs and found that increases in amino acid substitution in the P1 capsid protein resulted in a decrease in the neutralizing capacity of the sera. This study underscores the importance of maintaining high vaccine coverage in areas of OPV use as well as active surveillance of those known to be immunocompromised.

Sequential inactivated (IPV) and live oral (OPV) poliovirus vaccines for preventing poliomyelitis.

Sequential inactivated (IPV) and live oral (OPV) poliovirus vaccines for preventing poliomyelitis.

La batalla de Madrid por las vacunas antipoliomielitis (1963): ciencia, ideología y poder en la primera campaña de inmunización masiva en España

Between 1958 and 1963, Spain witnessed the highest ever incidence of poliomyelitis (2000 cases and 200 deaths per year). Although Salk's inactivated vaccine had arrived in Spain in 1957, the government took no decisive action to administer it to the entire population at risk. Neither was Sabin's attenuated vaccine administered, available in Europe from 1960. While other countries adopted one or the other, in Spain rivalry arose over the two vaccines, with mixed results. The Salk vaccine was administered to a small percentage of the population at risk through the Compulsory Sickness Insurance scheme (Spanish initials: SOE), while at the same time a research team at the National School of Health led by Florencio Pérez Gallardo (1917-2006) carried out a model epidemiological study that demonstrated the superiority of the Sabin vaccine. In 1963, the SOE launched a national campaign with the Salk vaccine promoted by the paediatrician Juan Bosch Marín (1902-1995), a representative of the most conservative structure of the Franco regime. The dispute over which vaccine was best reached its peak in early 1963 at various scientific conferences in Madrid. Bosch Marín's group argued in favour of his campaign and the Salk vaccine, while Pérez Gallardo did the same for the oral vaccine, achieving a substantial impact by inviting Sabin himself to speak. By the end of the year, following a pilot study, the first mass oral vaccination campaign against polio was introduced in Spain.

Risk factors and short-term projections for serotype-1 poliomyelitis incidence in Pakistan: A spatiotemporal analysis.

BackgroundPakistan currently provides a substantial challenge to global polio eradication, having contributed to 73% of reported poliomyelitis in 2015 and 54% in 2016. A better understanding of the risk factors and movement patterns that contribute to poliovirus transmission across Pakistan would support evidence-based planning for mass vaccination campaigns.Methods and findingsWe fit mixed-effects logistic regression models to routine surveillance data recording the presence of poliomyelitis associated with wild-type 1 poliovirus in districts of Pakistan over 6-month intervals between 2010 to 2016. To accurately capture the force of infection (FOI) between districts, we compared 6 models of population movement (adjacency, gravity, radiation, radiation based on population density, radiation based on travel times, and mobile-phone based). We used the best-fitting model (based on the Akaike Information Criterion [AIC]) to produce 6-month forecasts of poliomyelitis incidence. The odds of observing poliomyelitis decreased with improved routine or supplementary (campaign) immunisation coverage (multivariable odds ratio [OR] = 0.75, 95% confidence interval [CI] 0.67–0.84; and OR = 0.75, 95% CI 0.66–0.85, respectively, for each 10% increase in coverage) and increased with a higher rate of reporting non-polio acute flaccid paralysis (AFP) (OR = 1.13, 95% CI 1.02–1.26 for a 1-unit increase in non-polio AFP per 100,000 persons aged <15 years). Estimated movement of poliovirus-infected individuals was associated with the incidence of poliomyelitis, with the radiation model of movement providing the best fit to the data. Six-month forecasts of poliomyelitis incidence by district for 2013–2016 showed good predictive ability (area under the curve range: 0.76–0.98). However, although the best-fitting movement model (radiation) was a significant determinant of poliomyelitis incidence, it did not improve the predictive ability of the multivariable model. Overall, in Pakistan the risk of polio cases was predicted to reduce between July–December 2016 and January–June 2017. The accuracy of the model may be limited by the small number of AFP cases in some districts.ConclusionsSpatiotemporal variation in immunization performance and population movement patterns are important determinants of historical poliomyelitis incidence in Pakistan; however, movement dynamics were less influential in predicting future cases, at a time when the polio map is shrinking. Results from the regression models we present are being used to help plan vaccination campaigns and transit vaccination strategies in Pakistan.

Estimated Effect of Inactivated Poliovirus Vaccine Campaigns, Nigeria and Pakistan, January 2014-April 2016.

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.

Eradicating polio in Pakistan: an analysis of the challenges and solutions to this security and health issue.

Since the launch of the Global Polio Eradication Initiative (GPEI) in 1988 the global incidence of poliomyelitis has fallen by nearly 99 %. From a situation where wild type poliovirus was endemic in 125 countries across five continents, transmission is now limited to regions of just three countries – Pakistan, Afghanistan and Nigeria. A sharp increase in Pakistan’s poliomyelitis cases in 2014 prompted the International Health Regulations Emergency Committee to declare the situation a ‘public health emergency of international concern’. Global polio eradication hinges on Pakistan’s ability to address the religious, political and socioeconomic barriers to immunisation; including discrepancies in vaccine coverage, a poor health infrastructure, and conflict in polio-endemic regions of the country. This analysis provides an overview of the GPEI, focusing on the historical and contemporary challenges facing Pakistan’s polio eradication programme and the impact of conflict and insecurity, and sheds light on strategies to combat vaccine hesitancy, engage local communities and build on recent progress towards polio eradication in Pakistan.

Vaccine-Derived Polioviruses and Children with Primary Immunodeficiency, Iran, 1995-2014.

Widespread use of oral poliovirus vaccine has led to an ≈99.9% decrease in global incidence of poliomyelitis (from ≈350,000 cases in 1988 to 74 cases in 2015) and eradication of wild-type poliovirus serotypes 2 and 3. However, patients with primary immunodeficiency might shed vaccine-derived polioviruses (VDPVs) for an extended period, which could pose a major threat to polio eradication programs. Since 1995, sixteen VDPV populations have been isolated from 14 patients with immunodeficiency in Iran. For these patients, vaccine-associated paralysis, mostly in >1 extremity, was the first manifestation of primary immunodeficiency. Seven patients with humoral immunodeficiency cleared VDPV infection more frequently than did 6 patients with combined immunodeficiencies. Our results raise questions about manifestations of VDPVs in immunodeficient patients and the role of cellular immunity against enterovirus infections. On the basis of an association between VDPVs and immunodeficiency, we advocate screening of patients with primary immunodeficiency for shedding of polioviruses.

Spatial Dynamics and High Risk Transmission Pathways of Poliovirus in Nigeria 2001-2013.

The polio eradication programme in Nigeria has been successful in reducing incidence to just six confirmed cases in 2014 and zero to date in 2015, but prediction and management of future outbreaks remains a concern. A Poisson mixed effects model was used to describe poliovirus spread between January 2001 and November 2013, incorporating the strength of connectivity between districts (local government areas, LGAs) as estimated by three models of human mobility: simple distance, gravity and radiation models. Potential explanatory variables associated with the case numbers in each LGA were investigated and the model fit was tested by simulation. Spatial connectivity, the number of non-immune children under five years old, and season were associated with the incidence of poliomyelitis in an LGA (all P < 0.001). The best-fitting spatial model was the radiation model, outperforming the simple distance and gravity models (likelihood ratio test P < 0.05), under which the number of people estimated to move from an infected LGA to an uninfected LGA was strongly associated with the incidence of poliomyelitis in that LGA. We inferred transmission networks between LGAs based on this model and found these to be highly local, largely restricted to neighbouring LGAs (e.g. 67.7% of secondary spread from Kano was expected to occur within 10 km). The remaining secondary spread occurred along routes of high population movement. Poliovirus transmission in Nigeria is predominantly localised, occurring between spatially contiguous areas. Outbreak response should be guided by knowledge of high-probability pathways to ensure vulnerable children are protected.

Poliovirus Laboratory Based Surveillance: An Overview.

World Health Assembly (WHA) in 1988 encouraged the member states to launch Global Polio Eradication Initiative (GPEI) (resolution WHA41.28) against "the Crippler" called poliovirus, through strong routine immunization program and intensified surveillance systems. Since its launch, global incidence of poliomyelitis has been reduced by more than 99 % and the disease squeezed to only three endemic countries (Afghanistan, Pakistan, and Nigeria) out of 125. Today, poliomyelitis is on the verge of eradication, and their etiological agents, the three poliovirus serotypes, are on the brink of extinction from the natural environment. The last case of poliomyelitis due to wild type 2 strain occurred in 1999 in Uttar Pradesh, India whereas the last paralytic case due to wild poliovirus type 3 (WPV3) was seen in November, 2012 in Yobe, Nigeria. Despite this progress, undetected circulation cannot fully rule out the eradication as most of the poliovirus infections are entirely subclinical; hence sophisticated environmental surveillance is needed to ensure the complete eradication of virus. Moreover, the vaccine virus in under-immunized communities can sometimes revert and attain wild type characteristics posing a big challenge to the program.

Circulating vaccine-derived poliovirus type 2 outbreak in Democratic Republic of Congo 2011-2012

According to the WHO records of 2013, the incidence of poliomyelitis was reduced by more than 99%, the number of endemic countries decreased from 125 in 1988 to 3 in 2013 and over 10 million cases were prevented from poliomyelitis thanks to the intensive use of Oral polio vaccine (OPV). However, the emergence of circulating vaccine-derived poliovirus strains (cVDPV), causing serious epidemics like the wild poliovirus, is a major challenge on the final straight towards the goal of eradication and OPV cessation. This paper describes the cVDPVoutbreak that occurred in the Democratic Republic of Congo (DRC) from November 2011 to April 2012. All children under 15 years of age with acute flaccid paralysis (AFP) and confirmed presence of cVDPV in the stool samples were included. Thirty (30) children, all from the administrative territories of Bukama and Malemba Nkulu in the Katanga Province (south-east DRC), were reported. The virus responsible was the cVDPV type 2 (0.7% -3.5% divergent from the reference Sabin 2 strain) in 29 children (97%) and the ambiguous vaccine-derived poliovirus strain (0.7% divergent) was confirmed in one case (3%), a boy seventeen months old and already vaccinated four times with OPV. Twentyfive children (83%) were protected by any of the routine EPI vaccines and 3 children (10%) had never received any dose of OPV. In reaction, DRC has conducted five local campaigns over a period of 10 months (from January to October 2012) and the epidemic was stopped after the second round performed in March 2012. As elsewhere in similar conditions, low immunization coverage, poor sanitation conditions and the stop of the use of OPV2 have favoured the emergence of the third cVDPV epidemic in DRC. The implementation of the Strategic Plan for Polio eradication and endgame strategic plan 2013-2018 will prevent the emergence of cVDPV and set up the conditions for a coordinated OPV phase out.

Post-polio eradication: vaccination strategies and options for India

In 1988, the World Health Organization (WHO) resolved to eradicate poliomyelitis globally. Since then, the initiative has reported dramatic progress in decreasing the incidence of poliomyelitis and limiting the geographical extent of transmission. 2013 is recorded as the second consecutive year not reporting wild poliovirus (WPV) from India. If the country can retain this position for one more year India will be declared as polio eradicated. What should be the future vaccination strategies? We searched and reviewed the full text of the available published literature on polio eradication via PubMed and examined Internet sources and websites of major international health agencies. The oral polio vaccine (OPV) has been the main tool in the polio eradication program. Once WPV transmission is interrupted, the poliomyelitis will be caused only by OPV. India could expect 1 vaccine-associated paralytic polio per 4.2-4.6 million doses of OPV. Considering the threat of vaccine-derived viruses to polio eradication, WHO urged to develop a strategy to safely discontinue OPV after certification. The ultimate aim is to stop OPV safely and effectively, and eventually substitute with inactivated polio vaccine (IPV). The argument against the use of IPV is its cost. From India, field based data were available on the efficacy of IPV, which was better than OPV. IPV given intradermally resulted in seroconversion rates similar to full-dose intramuscular vaccine. The incremental cost of adopting IPV to replace OPV is relatively low, about US $1 per child per year, and most countries should be able to afford this additional cost.

The role of older children and adults in wild poliovirus transmission

As polio eradication inches closer, the absence of poliovirus circulation in most of the world and imperfect vaccination coverage are resulting in immunity gaps and polio outbreaks affecting adults. Furthermore, imperfect, waning intestinal immunity among older children and adults permits reinfection and poliovirus shedding, prompting calls to extend the age range of vaccination campaigns even in the absence of cases in these age groups. The success of such a strategy depends on the contribution to poliovirus transmission by older ages, which has not previously been estimated. We fit a mathematical model of poliovirus transmission to time series data from two large outbreaks that affected adults (Tajikistan 2010, Republic of Congo 2010) using maximum-likelihood estimation based on iterated particle-filtering methods. In Tajikistan, the contribution of unvaccinated older children and adults to transmission was minimal despite a significant number of cases in these age groups [reproduction number, R = 0.46 (95% confidence interval, 0.42-0.52) for >5-y-olds compared to 2.18 (2.06-2.45) for 0- to 5-y-olds]. In contrast, in the Republic of Congo, the contribution of older children and adults was significant [R = 1.85 (1.83-4.00)], perhaps reflecting sanitary and socioeconomic variables favoring efficient virus transmission. In neither setting was there evidence for a significant role of imperfect intestinal immunity in the transmission of poliovirus. Bringing the immunization response to the Tajikistan outbreak forward by 2 wk would have prevented an additional 130 cases (21%), highlighting the importance of early outbreak detection and response.

Foot Drop of Contralateral Limb after Deformity Correction in a Polio Patient: A Case Report

Postpoliomyelitis syndrome is a common neurological disorder that occurs in patients who have experienced paralytic poliomyelitis. Recently, as a result of vaccination against poliovirus, incidence of poliomyelitis is exceedingly low. However, many patients with postpolio syndrome may encounter anesthesia when undergoing surgery, such as for correction of foot deformity and other operations. We report on a 45-year-old woman who experienced paralysis of her contralateral limb after operation on the left foot under spinal anesthesia. Postoperative electromyography/nerve conduction study (EMG/NCS) was performed in order to determine the cause of paralysis. Motor power of the sequelae involved leg showed improvement with time and recovered fully to the preoperative level at six months after the index operation. A precise evaluation, including a physical examination and EMG/NCS, should be performed preoperatively when spinal anesthesia is planned for postpolio syndrome patients.

The final stages of the global eradication of poliomyelitis

The global incidence of poliomyelitis has dropped by more than 99 per cent since the governments of the world committed to eradication in 1988. One of the three serotypes of wild poliovirus has been eradicated and the remaining two serotypes are limited to just a small number of endemic regions. However, the Global Polio Eradication Initiative (GPEI) has faced a number of challenges in eradicating the last 1 per cent of wild-virus transmission. The polio endgame has also been complicated by the recognition that vaccination with the oral poliovirus vaccine (OPV) must eventually cease because of the risk of outbreaks of vaccine-derived polioviruses. I describe the major challenges to wild poliovirus eradication, focusing on the poor immunogenicity of OPV in lower-income countries, the inherent limitations to the sensitivity and specificity of surveillance, the international spread of poliovirus and resulting outbreaks, and the potential significance of waning intestinal immunity induced by OPV. I then focus on the challenges to eradicating all polioviruses, the problem of vaccine-derived polioviruses and the risk of wild-type or vaccine-derived poliovirus re-emergence after the cessation of oral vaccination. I document the role of research in the GPEI's response to these challenges and ultimately the feasibility of achieving a world without poliomyelitis.

Neutralization Antibodies in Oral Poliovirus Vaccine (OPV) Vaccinated Children and Young Adult in Bida North Central, Nigeria

Following the widespread use of Poliovirus Vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries. While now rare in the western world, Polio is still endemic to South Asia and Nigeria. This is no doubt a burden to the Federal Government of Nigeria. This work studied the serological response of OPV trivalent formulation in order to observe the Seroconversion rate among the OPV recipients in Bida, Niger State North Central Nigeria using Neutrali- zation Method. Samples were collected from 200 children and young adults that have been immunized with Oral Poliovirus Vaccine in Bida community. Participants are within the 1 st day to 15 years of age. There was no significant statistical difference between poliovirus serotypes and sex (P > 0.05). It was observed that 60% of the 5 neonates (age less than 4 weeks) that parti- cipated in the study with zero dose or first dose has antibody titer level> 1:8 for more than two poliovirus serotypes, while 57.14 % of the 7 infants less than 10 weeks ( 1:8 for more than two poliovirus serotypes. The responsiveness against poliovirus vaccine varied much between children at different ages. It was observed that there were low mean titer values for the three serotypes in age group 5.1 -10years and 10.1 - 15years compared to age groups below5years. It was also discovered that some of the studied cases have no protective level of antibodies which represent a high risk factor if they are exposed to clinical doses of wild poliovirus with seronegativity rates for PV1=43.68%, PV2=45.37%, PV3=44.07%. Therefore, it is recommended that indigenous vaccine production, repeat vaccination among children below5 years and measurement of protective antibodies against poliovirus at different intervals to ascertain both the immune status of the vaccine recipients and the validity of the vaccine, be encouraged.

Certification of Poliomyelitis Eradication in Singapore and the Challenges Ahead

This study reviewed the epidemiological trends of poliomyelitis from 1946 to 2010, and the impact of the national immunisation programme in raising the population herd immunity against poliovirus. We also traced the efforts Singapore has made to achieve certification of poliomyelitis eradication by the World Health Organisation. Epidemiological data on all reported cases of poliomyelitis were obtained from the Communicable Diseases Division of the Ministry of Health as well as historical records. Coverage of the childhood immunisation programme against poliomyelitis was based on the immunisation data maintained by the National Immunisation Registry, Health Promotion Board. To assess the herd immunity of the population against poliovirus, 6 serological surveys were conducted in 1962, 1978, 1982 to 1984, 1989, 1993 and from 2008 to 2010. Singapore was among the fi rst countries in the world to introduce live oral poliovirus vaccine (OPV) on a mass scale in 1958. With the comprehensive coverage of the national childhood immunisation programme, the incidence of paralytic poliomyelitis declined from 74 cases in 1963 to 5 cases from 1971 to 1973. The immunisation coverage for infants, preschool and primary school children has been maintained at 92% to 97% over the past decade. No indigenous poliomyelitis case had been reported since 1978 and all cases reported subsequently were imported. Singapore was certified poliomyelitis free along with the rest of the Western Pacific Region in 2000 after fulfilling all criteria for poliomyelitis eradication, including the establishment of a robust acute flaccid paralysis surveillance system. However, post-certification challenges remain, with the risk of wild poliovirus importation. Furthermore, it is timely to consider the replacement of OPV with the inactivated poliovirus vaccine in Singapore's national immunisation programme given the risk of vaccine-associated paralytic poliomyelitis and circulating vaccine-derived polioviruses.

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

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.