Seroprevalence of anti-polio antibodies in children from polio high risk area of Afghanistan: A cross sectional survey 2017

Exploring the path to polio eradication: insights from consecutive seroprevalence surveys among Pakistani children

Introduction

After trivalent oral poliovirus vaccine (tOPV) cessation, Pakistan has maintained immunity to type 2 poliovirus by administering inactivated polio vaccine (IPV) in routine immunization, alongside monovalent OPV type 2 (mOPV2) and IPV in supplementary immunization activities (SIAs). This study assesses the change in poliovirus type 2 immunity after tOPV withdrawal and due to SIAs with mOPV2 and IPV among children aged 6-11 months.

Methods

Three cross-sectional sequential serological surveys were conducted in 12 polio high-risk areas of Pakistan. 25 clusters from each geographical stratum were selected utilizing probability proportional to size.

Results

Seroprevalence of type 2 poliovirus was 49%, with significant variation observed among surveyed areas; <30% in Pishin, >80% in Killa Abdullah, Mardan & Swabi, and Rawalpindi. SIAs with IPV improved immunity from 38 to 57% in Karachi and 60 to 88% in Khyber. SIAs with IPV following mOPV2 improved immunity from 62 to 65% in Killa Abdullah, and combined mOPV2 and IPV SIAs in Pishin improved immunity from 28 to 89%. Results also reflected that immunity rates for serotypes 1 and 3 were consistently above 90% during all three phases and across all geographical areas.

Conclusion

The study findings highlight the importance of implementing effective vaccination strategies to prevent the re-emergence of poliovirus. Moreover, the results provide crucial information for policymakers working toward achieving global polio eradication.

Poliovirus serological assay after the cVDPV1 outbreak in Papua New Guinea: a cross-sectional study from 2020 to 2021

Background

In June 2018, a type 1 circulating vaccine-derived poliovirus (cVDPV1) outbreak was declared in Papua New Guinea (PNG), resulting in a total of 26 paralytic confirmed cases. Eight vaccination campaign rounds with bivalent oral poliovirus vaccine (bOPV) were carried out in response. Prevalence of neutralizing polio antibodies in children was assessed two years after the outbreak response was completed.

Methods

We conducted a cross-sectional serological survey among children aged 6 months-10 years selected from six provinces in PNG to evaluate seroprevalence of neutralizing polio antibodies to the three poliovirus serotypes and analyse sociodemographic risk factors.

Findings

We included 984 of 1006 enrolled children in the final analysis. The seroprevalence of neutralizing polio antibodies for serotype 1, 2 and 3 was 98.3% (95% CI: 97.4-98.9), 63.1% (95% CI: 60.1-66.1) and 95.0% (95% CI: 93.6-96.3), respectively. Children <1 year had significantly lower type 1 seroprevalence compared to older children (p < 0.001); there were no significant differences in seroprevalence among provinces.

Interpretation

PNG successfully interrupted transmission of cVDPV1 with several high coverage bOPV campaigns and seroprevalence remained high after two years. The emergence of cVDPV strains underscores the importance of maintaining high levels of routine immunization coverage and effective surveillance systems for early detection.

Funding

World Health Organization through a Rotary International IPPC grant.

Immunity to poliovirus in Afghanistan: A household sampling method for serological assessment based on geographical information systems

Afghanistan continues to experience challenges affecting polio eradication. Mass polio vaccination campaigns, which aim to protect children under the age of 5, are a key eradication strategy. To date, the polio program in Afghanistan has only employed facility-based seroprevalence surveys, which can be subject to sampling bias. We describe the feasibility in implementing a cross-sectional household poliovirus seroprevalence survey based on geographical information systems (GIS) in three districts. Digital maps with randomly selected predetermined starting points were provided to teams, with a total target of 1,632 households. Teams were instructed to navigate to predetermined starting points and enrol the closest household within 60 m. To assess effectiveness of these methods, we calculated percentages for total households enrolled with valid geocoordinates collected within the designated boundary, and whether the Euclidean distance of households were within 60 m of a predetermined starting point. A normalized difference vegetation index (NDVI) image ratio was conducted to further investigate variability in team performances. The study enrolled a total of 78% of the target sample with 52% of all households within 60 m of a pre-selected point and 79% within the designated cluster boundary. Success varied considerably between the four target areas ranging from 42% enrolment of the target sample in one place to 90% enrolment of the target sample in another. Interviews with the field teams revealed that differences in security status and amount of non-residential land cover were key barriers to higher enrolment rates. Our findings indicate household poliovirus seroprevalence surveys using GIS-based sampling can be effectively implemented in polio endemic countries to capture representative samples. We also proposed ways to achieve higher success rates if these methods are to be used in the future, particularly in areas with concerns of insecurity or spatially dispersed residential units.

Poliovirus Immunity among Children Aged 6-11 and 36-48 Months in 14 Polio High-Risk Provinces of Afghanistan: A Health-Facility-Based Study

Afghanistan is one of two countries where wild poliovirus (WPV) type 1 remains endemic. We conducted a facility-based cross-sectional survey of antipoliovirus antibodies in children in 14 provinces of Afghanistan. The provinces were selected based on programmatic priorities for polio eradication. Children aged 6–11 and 36–48 months attending outpatient clinics were enrolled in the study. We collected venous blood, isolated serum, and conducted neutralization assays to detect poliovirus neutralizing antibodies. A total of 2086 children from the 14 provinces were enrolled. Among the enrolled children, 44.3% were girls; the median age in the 6–11-month group was 9.4 months, and in the 36–48-month group, it was 41.8 months. The most common spoken language was Pashtu (70.8%). Eighty-two percent of children were fully immunized against all the diseases in the vaccination schedule of Afghanistan. In the children aged 6–11 months, seroprevalence to poliovirus type 1 (PV1) was 96.5% and seroprevalence to poliovirus type 3 (PV3) was 93%; in children aged 36–48 months, seroprevalence to PV1 was 99.5% and to PV3 was 98%. Antipoliovirus antibody prevalence for poliovirus type 2 (PV2) was 70.5% in the younger group compared with 90.9% in the older children. Children from Herat and Laghman provinces had almost 100% seroprevalence to PV1, and other provinces also had high prevalence, ranging from 92.0% to 99.0%. A similar finding was seen for antibodies against PV3, ranging from 88% to 100% by province. On the contrary, antibodies to PV2 were low, ranging from 53% for children in the Khost province to around 89% in Kunduz. There was a cluster of 18 seronegative children in the Nuristan province. Overall, the polio eradication program of Afghanistan has been successful in achieving high seroprevalence of poliovirus neutralizing antibodies in the parts of the country included in this study.

Implication of a High Risk for Type 2 Vaccine-Derived Poliovirus Emergence and Transmission After the Switch From Trivalent to Bivalent Oral Poliovirus Vaccine

BACKGROUND

China implemented the globally synchronized switch from trivalent oral poliovirus vaccine (tOPV) to bivalent OPV (bOPV) and introduced 1 dose of inactivated poliovirus vaccine on 1 May 2016. We assessed the impact of the switch on the immunity level against poliovirus, especially type 2.

METHODS

Children born between 2014 and 2017, who were brought to the hospitals in Urumqi city, Xinjiang Province in 2017, were enrolled and blood samples were collected to test for antibody titers against poliovirus. A comparison of seroprevalence between the children born before (preswitch group) and after the switch (postswitch group) was performed to assess the impact of the switch on the immunity level against polio.

RESULTS

A total of 172 subjects were enrolled. The overall seroprevalences were 98.8%, 79.1%, and 98.3% for types 1, 2, and 3, respectively. Seroprevalence for type 2 significantly decreased from 91.6% in the preswitch group to 67.4% in the postswitch group, but no statistically significant change was observed for both types 1 and 3.

CONCLUSIONS

The switch from tOPV to bOPV can provide high-level immunity against types 1 and 3 but not against type 2, indicating a high risk of type 2 vaccine-derived poliovirus emergence and transmission.

High coverage of polio immunization program in refugees resettling in Denmark. A cross-sectional study of polio serology in newly arrived refugees

Objectives: Wild poliovirus (WPV) infection has been eliminated in Europe through mass immunization. Resettling refugees may lack immunity and importing WPV through refugees continues to cause concerns.Method: We performed a cross-sectional study to establish the prevalence of poliovirus immunity in children and adult refugees resettling in Aarhus, Denmark. Immunity was evaluated by antibody response for serotypes 1, 2, and 3.Results: The participants in this study counted a total of 475 children and adult refugees aged between 6 months and 76 years and 59% were males. The survey was conducted between 2014 and 2016. Among the refugees, 72% were from Syria, and the rest from Eritrea, Congo, Lebanon, Somalia, Afghanistan, Iran, Iraq, Ethiopia, and Columbia. In the cohort, 27 lacked antibodies against a least one serotype. None of the participants lacked antibodies against all three polio types. Originating from The Horn of Africa, age between 20 and 30 and male gender was associated with lack of immunity.Conclusion: The study found a complete WPV immunity in 94% of recently resettled refugees in Denmark. This study demonstrates a high coverage of the polio immunization program. However, ensuring poliovirus immunity among refugees remains a priority until polio has been eradicated worldwide.

Poliovirus immunity among children under five years-old in accessible areas of Afghanistan, 2013

BACKGROUND

Afghanistan remains among the three countries with endemic wild poliovirus transmission, and high population immunity levels are required to interrupt transmission and prevent outbreaks. Surveillance and vaccination of children in Afghanistan have been challenging due to security issues limiting accessibility in certain areas.

METHODS

A serosurvey was conducted in 2013 within accessible enumeration areas (EAs) among children aged <5 years using samples collected for a national micronutrient assessment survey to assess poliovirus immunity in Afghanistan. Of 21194 total EAs in Afghanistan, 107 were inaccessible and therefore were excluded from the sampling frame.

RESULTS

Population immunity was high overall but varied for the poliovirus serotypes, and was lowest for type 3 (95% [95% CI: 93%, 96%]) compared to type 1 (99% [95% CI:97%, 99%]) and type 2 (98% [95% CI:96%, 99%]). The proportion of the population immune to all three types was 93% (95% CI: 91%, 95%), and the proportion seronegative for all three types was 0.5% (95% CI: 0.2%, 1.7%).

CONCLUSION

Except for regional differences in immunity to type 3 virus, there were no other apparent differences in seroprevalence by region or by any of the demographic or nutritional characteristics assessed in this study. The study was not powered to provide provincial level seroprevalence estimates, but Paktika Province, in the South region, had the largest proportion of seronegative specimens for type 1 (4 seronegative of 17 serum specimens compared to 14 seronegative of 673 for the remainder of the areas). Among accessible children in Afghanistan, seroprevalence of antibodies to poliovirus was high, with most seroprevalence reported at 95% or greater. Despite high seroprevalence in areas assessed in this study, the continued detection of poliovirus cases in the South and East regions indicate that overall regional vaccination coverage and performance is not sufficient to stop polio transmission.