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Abstract Background To assess the immunogenicity of the current primary polio vaccination schedule in China and compare it with alternative schedules using Sabin or Salk-strain IPV (sIPV, wIPV). Methods A cross-sectional investigation was conducted at four sites in Chongqing, China, healthy infants aged 60–89 days were conveniently recruited and divided into four groups according to their received primary polio vaccination schedules (2sIPV + bOPV, 2wIPV + bOPV, 3sIPV, and 3wIPV). The sero-protection and neutralizing antibody titers against poliovirus serotypes (type 1, 2, and 3) were compared after the last dose. Results There were 408 infants completed the protocol. The observed seropositivity was more than 96% against poliovirus types 1, 2, and 3 in all groups. IPV-only groups induced higher antibody titers(GMT) against poliovirus type 2 (Median:192, QR: 96–384, P

Background: To assess the immunogenicity of the current primary polio vaccination schedule in China and compare it with alternative schedules using Sabin or Salk-strain IPV (sIPV, wIPV). Methods: A cross-sectional investigation was conducted at four sites in Chongqing, China, healthy infants aged 60–89 days were conveniently recruited and divided into four groups according to their received primary polio vaccination schedules (2sIPV + bOPV, 2wIPV + bOPV, 3sIPV, and 3wIPV). The sero-protection and neutralizing antibody titers against poliovirus serotypes (type 1, 2, and 3) were compared after the last dose. Results: There were 408 infants completed the protocol. The observed seropositivity was more than 96% against poliovirus types 1, 2, and 3 in all groups. IPV-only groups induced higher antibody titers(GMT) against poliovirus type 2 (Median:192, QR: 96–384, P<0.05) than the "2IPV + bOPV" group. While the "2IPV + bOPV" group induced significantly higher antibody titers against poliovirus type 1 (Median:2048, QR: 768–2048, P<0.05)and type 3 (Median:2048, QR: 512–2048, P<0.05) than the IPV-only group. Conclusions: Our findings have proved that the two doses of IPV with one dose of bOPV is currently the best polio routine immunization schedule in China. [ABSTRACT FROM AUTHOR]

To inform response strategies, we examined type 1 humoral and intestinal immunity induced by 1) one fractional inactivated poliovirus vaccine (fIPV) dose given with monovalent oral poliovirus vaccine (mOPV1), and 2) mOPV1 versus bivalent OPV (bOPV). We conducted a randomized, controlled, open-label trial in Dhaka, Bangladesh. Healthy infants aged 5 weeks were block randomized to one of four arms: mOPV1 at age 6–10–14 weeks/fIPV at 6 weeks (A); mOPV1 at 6–10–14 weeks/fIPV at 10 weeks (B); mOPV1 at 6–10–14 weeks (C); and bOPV at 6–10–14 weeks (D). Immune response at 10 weeks and cumulative response at 14 weeks was assessed among the modified intention-to-treat population, defined as seroconversion from seronegative (<1:8 titers) to seropositive (≥1:8) or a four-fold titer rise among seropositive participants sustained to age 18 weeks. We examined virus shedding after two doses of mOPV1 with and without fIPV, and after the first mOPV1 or bOPV dose. The trial is registered at ClinicalTrials.gov (NCT03722004). During 18 December 2018 – 23 November 2019, 1,192 infants were enrolled (arms A:301; B:295; C:298; D:298). Immune responses at 14 weeks did not differ after two mOPV1 doses alone (94% [95% CI: 91–97%]) versus two mOPV1 doses with fIPV at 6 weeks (96% [93–98%]) or 10 weeks (96% [93–98%]). Participants who received mOPV1 and fIPV at 10 weeks had significantly lower shedding (p < 0·001) one- and two-weeks later compared with mOPV1 alone. Response to one mOPV1 dose was significantly higher than one bOPV dose (79% versus 67%; p < 0·001) and shedding two-weeks later was significantly higher after mOPV1 (76% versus 56%; p < 0·001) indicating improved vaccine replication. Ninety-nine adverse events were reported, 29 serious including two deaths; none were attributed to study vaccines. Given with the second mOPV1 dose, fIPV improved intestinal immunity but not humoral immunity. One mOPV1 dose induced higher humoral and intestinal immunity than bOPV. U.S. Centers for Disease Control and Prevention. [ABSTRACT FROM AUTHOR]

Introduction: This study assessed the seroprevalence against all three polioviruses among the last cohort of infants aged 6-11 months who received tOPV before the tOPV-bOPV switch and had an opportunity to receive a full dose of inactivated poliovirus vaccine introduced in the routine immunization schedule. Methods: Serum was tested for neutralizing antibodies against polioviruses among infants residing in three different risk- category states for poliovirus transmission in India viz., Bihar historically high-risk state for polio, Madhya Pradesh a State with low routine immunization coverage and Chhattisgarh with lower acute flaccid paralysis surveillance indicators. Results: A total of 1113 serum samples were tested across the three states. The overall seroprevalence was 98.5% (97.7-99.2), 98.9% (98.3-99.5) and 94.4% (93.0-95.8) for poliovirus types 1, 2 and 3 respectively. The median antibody titers for corresponding serotypes were 575, 362 and 181. Infants who received five doses of tOPV showed respective seroprevalence rates of 98.7%, 98.7% and 93.7% against types 1, 2 and 3 polioviruses. There was no significant difference in seroprevalence across the group of IPV recipients. The median reciprocal titers across the groups of IPV recipient was significantly higher (p = 0.006) for poliovirus-3. Conclusion: The seroprevalence rates observed in the study are historically the highest in the series of serosurveys that India has conducted to assess the population immunity against polioviruses. Poliovirus 2 seroprevalence was very high at the time of the tOPV-bOPV switch in India effected in April 2016.

Background and objectives: After using of trivalent oral poliovirus vaccine (OPV) for a long time in Iran, in recent years, due to the eradication of type 2 of poliovirus, a bivalent vaccine containing types 1 and 3 is used. Since it is a highly thermo labile vaccine strain of poliovirus, it should be stored under the recommended temperature. Because in vaccine storage and transportation, the cold chain may not be achieved in Iran tropical weather conditions, the potency of this vaccine may be subject to change. Methods: The purpose of this study was the stability evaluation of bivalent oral poliovirus vaccine produced by Razi Institute in Iran for stability study of vaccines to ensure constancy of virus at different temperatures and intervals freezing/defrosting cycles (stress tests). Three consecutive batches produced during full-scale production were sampled randomly. All quality control tests in the form of stability studies were done on vaccines stored at -20, 2-8, 22-25 and 35-37ºC in specific time intervals and 10, 20, 30, 40 and 50 freezing/defrosting cycles. Results: The findings indicate the stability of this vaccine in different situations. The results also showed the effects of the environment affecting factors on the potency of the vaccines and determined the correlation between the VVM grade and the vaccine potency. Conclusion: Important observations of the vaccine distribution network at different transit levels and the correlation of VVM grade and vaccine potency and freezing/defrosting are discussed in this study which will be of help to the vaccine program team.

• The last polio seroprevalence study in India before the tOPV-bOPV vaccine switch • Fraction IPV doses in routine immunization help to close immunity gaps • India had best immunity against polioviruses just before the tOPV-bOPV switch • Type 2 seroprevalence has been highest ever, just prior to the tOPV-bOPV switch • No cVDPV2 post tOPV- bOPV switch could be due to high population immunity This study assessed the seroprevalence against all three polioviruses among the last cohort of infants aged 6-11 months who received tOPV before the tOPV-bOPV switch and had an opportunity to receive a full dose of inactivated poliovirus vaccine introduced in the routine immunization schedule. Serum was tested for neutralizing antibodies against polioviruses among infants residing in three different risk- category states for poliovirus transmission in India viz., Bihar historically high-risk state for polio, Madhya Pradesh a State with low routine immunization coverage and Chhattisgarh with lower acute flaccid paralysis surveillance indicators. A total of 1113 serum samples were tested across the three states. The overall seroprevalence was 98.5% (97.7-99.2), 98.9% (98.3-99.5) and 94.4% (93.0-95.8) for poliovirus types 1, 2 and 3 respectively. The median antibody titers for corresponding serotypes were 575, 362 and 181. Infants who received five doses of tOPV showed respective seroprevalence rates of 98.7%, 98.7% and 93.7% against types 1, 2 and 3 polioviruses. There was no significant difference in seroprevalence across the group of IPV recipients. The median reciprocal titers across the groups of IPV recipient was significantly higher (p = 0.006) for poliovirus-3. The seroprevalence rates observed in the study are historically the highest in the series of serosurveys that India has conducted to assess the population immunity against polioviruses. Poliovirus 2 seroprevalence was very high at the time of the tOPV-bOPV switch in India effected in April 2016. [ABSTRACT FROM AUTHOR]

Abstract Background The globally synchronized switch from trivalent Oral Polio Vaccine (tOPV) to bivalent Oral Polio Vaccine (bOPV) took place in Nigeria on April 18th 2016. The country is divided into six geopolitical zones. This study reports the experiences and lessons learned from the switch process in the six states that make up Nigeria’s south-south geopolitical zone. Methods This was a descriptive retrospective review of Nigeria’s switch plan and structures used for implementing the tOPV-bOPV switch in the south-south zone. Nigeria’s National Polio Emergency Operation Centre (NPEOC) protocols, global guidelines and reports from switch supervisors during the switch were used to provide background information for this study. Quantitative data were derived from reviewing switch monitoring and validation documents as submitted to the NPEOC Results The switch process took place in all 3078 Health Facilities (HFs) and 123 Local Government Areas (LGAs) that make up the six states in the zone. A total of $139,430 was used for this process. The ‘healthcare personnel’ component received the highest budgetary allocation (59%) followed by the ‘logistics’ component (18%). Akwa Ibom state was allocated the highest number of healthcare personnel and hence received the most budgetary allocation compared to the six states (total healthcare personnel = 458, total budgetary allocation = $17,428). Validation of the switch process revealed that eight HFs in Bayelsa, Cross-River, Edo and Rivers states still possessed tOPV in cold-chain while six HFs in Cross-River and Rivers states had tOPV out of cold-chain but without the ‘do not use’ sticker. Akwa-Ibom was the only state in the zone to have bOPV and Inactivated Polio Vaccine (IPV) available in all its HFs monitored. Conclusion The Nigerian tOPV-bOPV switch was successful. For future Oral Polio Vaccine (OPV) withdrawals, implementation of the switch plan would be more feasible with an earlier dissemination of funds from global donor organizations, which would greatly aid timely planning and preparations. Increased budgetary allocation to the ‘logistics’ component to accommodate unexpected hikes in transportation prices and the general inefficiencies with power supply in the country is also advised.

• Four bOPV doses and 1 IPV dose resulted in high seroprotection for P1, P2, and P3. • Despite only had 1 dose of P2 in IPV, subjects have high seroprotection for P2. • There was no systemic event during 30 min after birth dose of bOPV. In this study, we aimed to evaluate the immunological protectivity of infants following four doses of bivalent oral polio vaccine (bOPV; Bio Farma), which were given simultaneously with DTwP-Hb-Hib (Pentabio®), along with one dose of inactivated poliovirus vaccine (IPV) at the fourth visit. A total of 143 newborn infants who fulfilled the inclusion criteria were enrolled and completed the study. Subjects received the first dose of bOPV at birth. On days 60, 90 and 120, bOPV was given simultaneously with Pentabio®. On day 120, one dose of IPV was also administered. Serum samples for serology analysis were collected before the first dose of bOPV (at day 0), before the second dose of bOPV (at day 60) and 30 days after the last dose of bOPV. In addition, the intensity, duration and relationship of each adverse event to the trial vaccines were assessed. Seroprotection rates after the fourth dose of bOPV were 100%, 91.6% and 99.3% for poliovirus P1, P2 and P3, respectively. Seroconversion rates after the fourth dose of bOPV were 100.0%, 93.3% and 100% for poliovirus P1, P2 and P3, respectively. There were no severe adverse events, and systemic reactions were generally mild during the 1–28 day post-vaccination period. Collectively, our findings indicate that bOPV given simultaneously with Pentabio® and one dose of IPV at the 4th visit was immunogenic and well tolerated. [ABSTRACT FROM AUTHOR]

Abstract In accordance with the end game strategies for polio eradication a synchronized switch plan from tOPV to bOPV was implemented globally in 2016. The National Committee for Polio Eradication (NCCPE) validated the switch activities in India. An expert group of 104 academics conducted field visits in 25 states and 2 Union territories for independent verification (after an initial round of verification by the National Polio Surveillance Project [NPSP]). The objectives were to validate withdrawal and disposal of tOPV by screening cold chain points in public and private sector health facilities in both rural and urban areas; additionally, availability of bOPV and IPV was also documented. 34 filled tOPV and 5 empty vials were detected inside cold chain equipment and 17 outside. The disposal mechanism was found to be reasonably adequate. The key strategies -- 'throttling' of vaccine supplies well ahead of the switch date while preventing stock outs at various immunization points, simultaneously working with the regulators to delicense the tOPV on the switch date and helping manufacturers to calibrate vaccine production according to national timelines, and strong and persistent advocacy with professional associations to align with national bOPV and IPV policy facilitated successful accomplishment of the switch process. Effective implementation of the switch strategy in India also bears testimony to the resilience of the health system operating under diverse and heterogeneous governance. [ABSTRACT FROM AUTHOR]

Background Quantifying interference of maternal antibodies with immune responses to varying dose schedules of inactivated polio vaccine (IPV) is important for the polio endgame as IPV replaces oral polio vaccine (OPV). Methods Type 2 poliovirus humoral and intestinal responses were analyzed using pre-IPV type 2 seropositivity as proxy for maternal antibodies from 2 trials in Latin America. Infants received 1 or 2 doses of IPV in sequential IPV–bivalent oral polio vaccine (bOPV) or mixed bOPV-IPV schedules. Results Among infants vaccinated with bOPV at age 6, 10, and 14 weeks of age and IPV at 14 weeks, those with type 2 pre-IPV seropositivity had lower seroprotection rates than seronegative infants at 4 weeks (92.7% vs 83.8%; difference, 8.9% [95% confidence interval, 0.6%–19.9%]; n = 260) and 22 weeks (82.7% vs 60.4%; difference, 22.3 [12.8%–32.4%]; n = 481) post-IPV. A second IPV at age 36 weeks resulted in 100% seroprotection in both groups. Among infants vaccinated with 1 IPV at age 8 weeks followed by 2 doses of bOPV, pre-IPV type 2-seropositive infants had lower seroprotection at age 28 weeks than those who were seronegative (93.0% vs 73.9%; difference, 19.6% [95% confidence interval, 7.3%–29.4%]; n = 168). A second dose of IPV at 16 weeks achieved >97% seroprotection at age 24 or 28 weeks, regardless of pre-IPV status. Poliovirus shedding after challenge with monovalent OPV, serotype 2, was higher in pre-IPV seropositive infants given sequential IPV-bOPV. No differences were observed in the mixed bOPV-IPV schedule. Conclusions The presence of maternal antibody is associated with lower type 2 post-IPV seroprotection rates among infants who receive a single dose of IPV. This impact persists until late in infancy and is overcome by a second IPV dose. [ABSTRACT FROM AUTHOR]

The World Health Organization, African Region is heading toward eradication of the three types of wild polio virus, from the Region. Cases of wild poliovirus (WPV) types 2 and 3 (WPV2 and WPV3) were last reported in 1998 and 2012, respectively, and WPV1 reported in Nigeria since July 2014 has been the last in the entire Region. This scenario in Nigeria, the only endemic country, marks a remarkable progress. This significant progress is as a result of commitment of key partners in providing the much needed resources, better implementation of strategies, accountability, and innovative approaches. This is taking place in the face of public emergencies and challenges, which overburden health systems of countries and threaten sustainability of health programmes. Outbreak of Ebola and other diseases, insecurity, civil strife and political instability led to displacement of populations and severely affected health service delivery. The goal of eradication is now within reach more than ever before and countries of the region should not relent in their efforts on polio eradication. WHO and partners will redouble their efforts and introduce better approaches to sustain the current momentum and to complete the job. The carefully planned withdrawal of oral polio vaccine type II (OPV2) with an earlier introduction of one dose of inactivated poliovirus vaccine (IPV), in routine immunization, will boost immunity of populations and stop cVDPVs. Environmental surveillance for polio viruses will supplement surveillance for AFP and improve sensitivity of detection of polio viruses. [ABSTRACT FROM AUTHOR]