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Continued emergence and spread of circulating vaccine-derived type 2 polioviruses and vaccine-associated paralytic poliomyelitis from Sabin oral poliovirus vaccines (OPVs) has stimulated development of two novel type 2 OPV candidates (OPV2-c1 and OPV2-c2) designed to have similar immunogenicity, improved genetic stability, and less potential to reacquire neurovirulence. We aimed to assess safety and immunogenicity of the two novel OPV candidates compared with a monovalent Sabin OPV in children and infants. We did two single-centre, multi-site, partly-masked, randomised trials in healthy cohorts of children (aged 1–4 years) and infants (aged 18–22 weeks) in Panama: a control phase 4 study with monovalent Sabin OPV2 before global cessation of monovalent OPV2 use, and a phase 2 study with low and high doses of two novel OPV2 candidates. All participants received one OPV2 vaccination and subsets received two doses 28 days apart. Parents reported solicited and unsolicited adverse events. Type 2 poliovirus neutralising antibodies were measured at days 0, 7, 28, and 56, and stool viral shedding was assessed up to 28 days post-vaccination. Primary objectives were to assess safety in all participants and non-inferiority of novel OPV2 day 28 seroprotection versus monovalent OPV2 in infants (non-inferiority margin 10%). These studies were registered with ClinicalTrials.gov, NCT02521974 and NCT03554798. The control study took place between Oct 23, 2015, and April 29, 2016, and the subsequent phase 2 study between Sept 19, 2018, and Sept 30, 2019. 150 children (50 in the control study and 100 of 129 assessed for eligibility in the novel OPV2 study) and 684 infants (110 of 114 assessed for eligibility in the control study and 574 of 684 assessed for eligibility in the novel OPV2 study) were enrolled and received at least one study vaccination. Vaccinations were safe and well tolerated with no causally associated serious adverse events or important medical events in any group. Solicited and unsolicited adverse events were overwhelmingly mild or moderate irrespective of vaccine or dose. Nearly all children were seroprotected at baseline, indicating high baseline immunity. In children, the seroprotection rate 28 days after one dose was 100% for monovalent OPV2 and both novel OPV2 candidates. In infants at day 28, 91 (94% [95% CI 87–98]) of 97 were seroprotected after receiving monovalent OPV2, 134 (94% [88–97]) of 143 after high-dose novel OPV2-c1, 122 (93% [87–97]) of 131 after low-dose novel OPV2-c1, 138 (95% [90–98]) of 146 after high-dose novel OPV2-c2, and 115 (91% [84–95]) of 127 after low-dose novel OPV2-c2. Non-inferiority was shown for low-dose and high-dose novel OPV2-c1 and high-dose novel OPV2-c2 despite monovalent OPV2 recipients having higher baseline immunity. Both novel OPV2 candidates were safe, well tolerated, and immunogenic in children and infants. Novel OPV2 could be an important addition to our resources against poliovirus given the current epidemiological situation. Fighting Infectious Diseases in Emerging Countries and Bill & Melinda Gates Foundation.

Objectives: The National Immunization Program allows using a different manufacturer's vaccine for follow-up doses when the same vaccine is unavailable. This study aimed to evaluate the safety and immunogenicity of administering a third dose of Sabin strain (sIPV) from a different manufacturer in infants who had previously received two doses of sIPV. Methods: This randomized, blinded, controlled trial enrolled 200 healthy infants (≤12 months) to assess the safety and immunogenicity of sequential vaccination, who were randomly assigned to receive a third dose of sIPV from either a different manufacturer (experimental group) or the same manufacturer as the first two doses (control group). The study took place in Xiaogan City, Hubei Province, China, from 20 May 2024 to 6 September 2024. Immunogenicity and safety were assessed using per-protocol and safety populations, respectively. Results: The seroconversion rates for poliovirus types 1, 2, and 3 were 79.52 %, 67.47 %, and 74.70 % in the experimental group, respectively, compared to 73.56 %, 49.43 %, and 63.22 % in the control group, with P-values of 0.360, 0.017, and 0.106, respectively. The most common systemic adverse event (AE) was fever, and no significant differences in the incidence of AEs between the two groups were observed. No serious adverse events related to vaccines were reported. Conclusion: Sequential vaccination with sIPV from different manufacturers demonstrated superior immunogenicity compared to the initial vaccine, with no significant safety differences, indicating that using vaccines from different manufacturers for sequential dosing is a feasible and effective option.

Replacing oral polio vaccines with inactivated polio vaccines (IPVs) is necessary to stop the potential transmission of vaccine-derived polio viruses. We aimed to compare the safety and immunogenicity of a dose-sparing IPV (ds-IPV) with a full-dose IPV in infants in Bangladesh. This double-blind, randomised, controlled, phase 3 study was done at two field sites in Bangladesh (Kamlapur and Matlab). Eligible participants were healthy infants aged 6–8 weeks, with parents who intended to reside in the area during the study period. Participants were randomly assigned (1:1:1:1) to receive either ds-IPV from one of the three lots (lot A, B, or C; Serum Institute of India, Pune, India) or an IPV (Serum Institute of India). Three intramuscular doses (0·5 mL) were administered at age 6, 10, and 14 weeks in addition to other standard vaccines. The study staff involved in safety evaluation, study procedures, parents of the participants, and the laboratory personnel were masked to the treatment allocations. The primary endpoint was seroconversion for poliovirus types 1, 2, and 3 at 28 days after the third dose, assessed in the per-protocol and full analysis populations. Solicited adverse events were collected up to 4 days after each vaccine dose and unsolicited adverse events and serious adverse events were collected up to 28 days after the third dose. This study is registered with ClinicalTrials.gov, NCT05163561, and is complete. Between Jan 9, 2022, and April 29, 2023, 1072 eligible participants were randomly assigned to receive ds-IPV (n=801) or IPV (n=267), of whom 1052 completed the study. 755 (96% [95% CI 94 to 97]) of 786 participants in the ds-IPV group versus 256 (97% [94 to 98]) of 265 participants in the IPV group had seroconversion for poliovirus type 1 (difference –0·55% [95% CI –3·05 to 1·95]). 744 (95% [93 to 96]) of 786 participants in the ds-IPV group versus 261 (98% [96 to 100]) of 265 participants in the IPV group had seroconversion for poliovirus type 2 (difference –3·83% [–6·48 to –1·19]). 765 (97% [96 to 98]) of 786 participants in the ds-IPV group versus 260 (98% [96 to 99]) of 265 participants in the IPV group had seroconversion for poliovirus type 3 (difference –0·78% [–2·73 to 1·16]). Solicited events were observed in 446 (56%) of 801 participants in the ds-IPV group and 143 (54%) of 267 participants in the IPV group. Unsolicited events were observed in 746 (93%) of 801 participants in the ds-IPV group and 250 (94%) of 267 participants in the IPV group. Serious adverse events were observed in 23 (3%) of 801 participants in the ds-IPV group and five (2%) of 267 participants in the IPV group. The common serious adverse events were pneumonia (n=10 in the ds-IPV group; n=3 in the IPV group), bronchiolitis (n=3 in the ds-IPV group; n=1 in the IPV group), and diarrhoea (n=3 in the ds-IPV group; n=1 in the IPV group). None of the unsolicited events and serious adverse events were causally related to the study vaccines. Delivery of three intramuscular doses of the novel ds-IPV vaccine is safe and immunologically non-inferior to the delivery of three intramuscular doses of IPV, and the dose sparing formulation might therefore become an attractive option for some national immunisation programmes due to lower expected vaccine costs. Serum Institute of India.

In 2012, the Strategic Advisory Group of Experts on Immunization (SAGE) recommended introduction of at least one inactivated poliovirus vaccine (IPV) dose in essential immunization programs. We evaluated systemic humoral and intestinal mucosal immunity of a sequential IPV-bivalent oral poliovirus vaccine (bOPV) schedule compared with a co-administration IPV + bOPV schedule in an open-label, randomized, controlled, non-inferiority, inequality trial in Dhaka, Bangladesh. Healthy infants aged 6 weeks were randomized to either: (A) IPV and bOPV at 6 and bOPV at 10 and 14 weeks (IPV + bOPV-bOPV-bOPV); or (B) IPV at 6 and bOPV at 10 and 14 weeks (IPV-bOPV-bOPV). Of 456 participants enrolled and randomly assigned during May–August 2015, 428 (94%) were included in the modified intention-to-treat analysis (arm A: 211, arm B: 217). Humoral immune responses did not differ at 18 weeks between study arms: type 1 (98% versus 96%; p = 0.42), type 2 (37% versus 39%; p = 0.77), and type 3 (97% versus 93%; p = 0.07). Virus shedding one week after the bOPV challenge dose in arm B was non-inferior to arm A (type 1 difference = −3% [90% confidence interval: −6 − 0.4%]; type 3 difference: −3% [−6 to −0.2%]). Twenty-six adverse events including seven serious adverse events were reported among 25 participants including one death; none were attributed to study vaccines. An IPV-bOPV-bOPV sequential schedule induced comparable systemic humoral immunity to all poliovirus types and types 1 and 3 intestinal mucosal immunity as an IPV + bOPV-bOPV-bOPV co-administration schedule.

Following the global eradication of wild poliovirus, countries using live attenuated oral poliovirus vaccines will transition to exclusive use of inactivated poliovirus vaccine (IPV) or fractional doses of IPV (f-IPV; a f-IPV dose is one-fifth of a normal IPV dose), but IPV supply and cost constraints will necessitate dose-sparing strategies. We compared immunisation schedules of f-IPV and IPV to inform the choice of optimal post-eradication schedule. This randomised open-label, multicentre, phase 3, non-inferiority trial was done at two centres in Panama and one in the Dominican Republic. Eligible participants were healthy 6-week-old infants with no signs of febrile illness or known allergy to vaccine components. Infants were randomly assigned (1:1:1:1, 1:1:1:2, 2:1:1:1), using computer-generated blocks of four or five until the groups were full, to one of four groups and received: two doses of intradermal f-IPV (administered at 14 and 36 weeks; two f-IPV group); or three doses of intradermal f-IPV (administered at 10, 14, and 36 weeks; three f-IPV group); or two doses of intramuscular IPV (administered at 14 and 36 weeks; two IPV group); or three doses of intramuscular IPV (administered at 10, 14, and 36 weeks; three IPV group). The primary outcome was seroconversion rates based on neutralising antibodies for poliovirus type 1 and type 2 at baseline and at 40 weeks (4 weeks after the second or third vaccinations) in the per-protocol population to allow non-inferiority and eventually superiority comparisons between vaccines and regimens. Three co-primary outcomes concerning poliovirus types 1 and 2 were to determine if seroconversion rates at 40 weeks of age after a two-dose regimen (administered at weeks 14 and 36) of intradermally administered f-IPV were non-inferior to a corresponding two-dose regimen of intramuscular IPV; if seroconversion rates at 40 weeks of age after a two-dose IPV regimen (weeks 14 and 36) were non-inferior to those after a three-dose IPV regimen (weeks 10, 14, and 36); and if seroconversion rates after a two-dose f-IPV regimen (weeks 14 and 36) were non-inferior to those after a three-dose f-IPV regimen (weeks 10, 14, and 36). The non-inferiority boundary was set at −10% for the lower bound of the two-sided 95% CI for the seroconversion rate difference.. Safety was assessed as serious adverse events and important medical events. This study is registered on ClinicalTrials.gov, NCT03239496. From Oct 23, 2017, to Nov 13, 2018, we enrolled 773 infants (372 [48%] girls) in Panama and the Dominican Republic (two f-IPV group n=217, three f-IPV group n=178, two IPV group n=178, and three IPV group n=200). 686 infants received all scheduled vaccine doses and were included in the per-protocol analysis. We observed non-inferiority for poliovirus type 1 seroconversion rate at 40 weeks for the two f-IPV dose schedule (95·9% [95% CI 92·0–98·2]) versus the two IPV dose schedule (98·7% [95·4–99·8]), and for the three f-IPV dose schedule (98·8% [95·6–99·8]) versus the three IPV dose schedule (100% [97·9–100]). Similarly, poliovirus type 2 seroconversion rate at 40 weeks for the two f-IPV dose schedule (97·9% [94·8–99·4]) versus the two IPV dose schedule (99·4% [96·4–100]), and for the three f-IPV dose schedule (100% [97·7–100]) versus the three IPV dose schedule (100% [97·9–100]) were non-inferior. Seroconversion rate for the two f-IPV regimen was statistically superior 4 weeks after the last vaccine dose in the 14 and 36 week schedule (95·9% [92·0–98·2]) compared with the 10 and 14 week schedule (83·2% [76·5–88·6]; p=0·0062) for poliovirus type 1. Statistical superiority of the 14 and 36 week schedule was also found for poliovirus type 2 (14 and 36 week schedule 97·9% [94·8–99·4] vs 10 and 14 week schedule 83·9% [77·2–89·2]; p=0·0062), and poliovirus type 3 (14 and 36 week schedule 84·5% [78·7–89·3] vs 10 and 14 week schedule 73·3% [65·8–79·9]; p=0·0062). For IPV, a two dose regimen administered at 14 and 36 weeks (99·4% [96·4–100]) was superior a 10 and 14 week schedule (88·9% [83·4–93·1]; p<0·0001) for poliovirus type 2, but not for type 1 (14 and 36 week schedule 98·7% [95·4–99·8] vs 10 and 14 week schedule 95·6% [91·4–98·1]), or type 3 (14 and 36 week schedule 97·4% [93·5–99·3] vs 10 and 14 week schedule 93·9% [89·3–96·9]). There were no related serious adverse events or important medical events reported in any group showing safety was unaffected by administration route or schedule. Our observations suggest that adequate immunity against poliovirus type 1 and type 2 is provided by two doses of either IPV or f-IPV at 14 and 36 weeks of age, and broad immunity is provided with three doses of f-IPV, enabling substantial savings in cost and supply. These novel clinical data will inform global polio immunisation policy for the post-eradication era. Bill & Melinda Gates Foundation.

To evaluate the immunogencity and safety for three immunization schedules of inactivated poliovirus vaccine (IPV) and bivalent oral poliovirus vaccine (bOPV) for providing a basis for further optimization of the polio sequential immunization schedule. To obtain immunogenicity data and to active surveillance the occurrence of adverse events following immunization (AEFI), healthy infants ≥ 2 months of age were randomly chosen in Hebei Province, and were divided into three groups to be vaccinated with IPV-bOPV-bOPV(Group a), IPV-IPV-bOPV(Group b) and IPV-IPV-IPV(Group c) at 2, 3 and 4 months of age respectively. AEFI cases related to poliomyelitis vaccines in Hebei province by passive surveillance from January 1, 2018 to December 31, 2022 were obtained from national adverse event following immunization surveillance system (NAEFISS). After basic immunization with polio vaccine, the positive conversion rate of neutralizing antibodies of types I, II and III were all > 97.00% and the positive rates were all > 98.00%, the geometric mean titer (GMT) was significantly higher than that before basic immunization, the GMT level of neutralizing poliovirus antibody after basic immunization was the highest in type I, followed by type III, and the lowest in type II. A total of 16 AEFI cases (2.52%) were reported by active surveillance, and 2903 AEFI cases (1.40%) were reported by passive surveillance. AEFI reported by both monitoring modalities were dominated by fever of common vaccine reactions. No rare serious adverse reactions like VAPP etc. were monitored and the overall regression was positive. All three immunization schedules for polio vaccine have demonstrated good immunogenicity and safety when administered to healthy populations.

Use of oral live-attenuated polio vaccines (OPV), and injected inactivated polio vaccines (IPV) has almost achieved global eradication of wild polio viruses. To address the goals of achieving and maintaining global eradication and minimising the risk of outbreaks of vaccine-derived polioviruses, we tested novel monovalent oral type-2 poliovirus (OPV2) vaccine candidates that are genetically more stable than existing OPVs, with a lower risk of reversion to neurovirulence. Our study represents the first in-human testing of these two novel OPV2 candidates. We aimed to evaluate the safety and immunogenicity of these vaccines, the presence and extent of faecal shedding, and the neurovirulence of shed virus. In this double-blind, single-centre phase 1 trial, we isolated participants in a purpose-built containment facility at the University of Antwerp Hospital (Antwerp, Belgium), to minimise the risk of environmental release of the novel OPV2 candidates. Participants, who were recruited by local advertising, were adults (aged 18–50 years) in good health who had previously been vaccinated with IPV, and who would not have any contact with immunosuppressed or unvaccinated people for the duration of faecal shedding at the end of the study. The first participant randomly chose an envelope containing the name of a vaccine candidate, and this determined their allocation; the next 14 participants to be enrolled in the study were sequentially allocated to this group and received the same vaccine. The subsequent 15 participants enrolled after this group were allocated to receive the other vaccine. Participants and the study staff were masked to vaccine groups until the end of the study period. Participants each received a single dose of one vaccine candidate (candidate 1, S2/cre5/S15domV/rec1/hifi3; or candidate 2, S2/S15domV/CpG40), and they were monitored for adverse events, immune responses, and faecal shedding of the vaccine virus for 28 days. Shed virus isolates were tested for the genetic stability of attenuation. The primary outcomes were the incidence and type of serious and severe adverse events, the proportion of participants showing viral shedding in their stools, the time to cessation of viral shedding, the cell culture infective dose of shed virus in virus-positive stools, and a combined index of the prevalence, duration, and quantity of viral shedding in all participants. This study is registered with EudraCT, number 2017-000908-21 and ClinicalTrials.gov, number NCT03430349. Between May 22 and Aug 22, 2017, 48 volunteers were screened, of whom 15 (31%) volunteers were excluded for reasons relating to the inclusion or exclusion criteria, three (6%) volunteers were not treated because of restrictions to the number of participants in each group, and 30 (63%) volunteers were sequentially allocated to groups (15 participants per group). Both novel OPV2 candidates were immunogenic and increased the median blood titre of serum neutralising antibodies; all participants were seroprotected after vaccination. Both candidates had acceptable tolerability, and no serious adverse events occurred during the study. However, severe events were reported in six (40%) participants receiving candidate 1 (eight events) and nine (60%) participants receiving candidate 2 (12 events); most of these events were increased blood creatinine phosphokinase but were not accompanied by clinical signs or symptoms. Vaccine virus was detected in the stools of 15 (100%) participants receiving vaccine candidate 1 and 13 (87%) participants receiving vaccine candidate 2. Vaccine poliovirus shedding stopped at a median of 23 days (IQR 15–36) after candidate 1 administration and 12 days (1–23) after candidate 2 administration. Total shedding, described by the estimated median shedding index (50% cell culture infective dose/g), was observed to be greater with candidate 1 than candidate 2 across all participants (2·8 [95% CI 1·8–3·5] vs 1·0 [0·7–1·6]). Reversion to neurovirulence, assessed as paralysis of transgenic mice, was low in isolates from those vaccinated with both candidates, and sequencing of shed virus indicated that there was no loss of attenuation in domain V of the 5ʹ-untranslated region, the primary site of reversion in Sabin OPV. We found that the novel OPV2 candidates were safe and immunogenic in IPV-immunised adults, and our data support the further development of these vaccines to potentially be used for maintaining global eradication of neurovirulent type-2 polioviruses. Bill & Melinda Gates Foundation.

Polio eradication needs a new routine immunisation schedule—three or four doses of bivalent type 1 and type 3 oral poliovirus vaccine (bOPV) and one dose of inactivated poliovirus vaccine (IPV), but no immunogenicity data are available for this schedule. We aimed to assess immunogenicity of this vaccine schedule. We did an open-label, randomised controlled trial in four centres in India. After informed consent was obtained from a parent or legally acceptable representative, healthy newborn babies were randomly allocated to one of five groups: trivalent OPV (tOPV); tOPV plus IPV; bOPV; bOPV plus IPV; or bOPV plus two doses of IPV (2IPV). The key eligibility criteria were: full-term birth (≥37 weeks of gestation); birthweight ≥2·5 kg; and Apgar score of 9 or more. OPV was administered at birth, 6 weeks, 10 weeks, and 14 weeks; IPV was administered intramuscularly at 14 weeks. The primary study objective was to investigate immunogenicity of the new vaccine schedule, assessed by seroconversion against poliovirus types 1, 2, and 3 between birth and 18 weeks in the per-protocol population (all participants with valid serology results on cord blood and at 18 weeks). Neutralisation assays tested cord blood and sera collected at 14 weeks, 18 weeks, 19 weeks, and 22 weeks by investigators masked to group allocation. This trial was registered with the India Clinical Trials Registry, number CTRI/2013/06/003722. Of 900 newborn babies enrolled between June 13 and Aug 29, 2013, 782 (87%) completed the per-protocol requirements. Between birth and age 18 weeks, seroconversion against poliovirus type 1 in the tOPV group occurred in 162 of 163 (99·4%, 95% CI 96·6–100), in 150 (98·0%, 94·4–99·6) of 153 in the tOPV plus IPV group, in 153 (98·7%, 95·4–99·8) of 155 in the bOPV group, in 155 (99·4%, 96·5–100) of 156 in the bOPV plus IPV group, and in 154 (99·4%, 96·5–100) of 155 in the bOPV plus 2IPV group. Seroconversion against poliovirus type 2 occurred in 157 (96·3%, 92·2–98·6) of 163 in the tOPV group, 153 (100%, 97·6–100·0) of 153 in the tOPV plus IPV group, 29 (18·7%, 12·9–25·7) of 155 in the bOPV group, 107 (68·6%, 60·7–75·8) of 156 in the bOPV plus IPV group, and in 121 (78·1%, 70·7–84·3) of 155 in the bOPV plus 2IPV group. Seroconversion against poliovirus type 3 was achieved in 147 (90·2%, 84·5–94·3) of 163 in the tOPV group, 152 (99·3%, 96·4–100) of 153 in the tOPV plus IPV group, 151 (97·4%, 93·5–99·3) of 155 in the bOPV group, 155 (99·4%, 96·5–100) of 156 in the bOPV plus IPV group, and 153 (98·7%, 95·4–99·8) of 155 in the bOPV plus 2IPV group. Superiority was achieved for vaccine regimens including IPV against poliovirus type 3 compared with those not including IPV (tOPV plus IPV vs tOPV alone, p=0·0008; and bOPV plus IPV vs bOPV alone, p=0·0153). 12 serious adverse events occurred (six in the tOPV group, one in the tOPV plus IPV group, three in the bOPV group, zero in the bOPV plus IPV group, and two in the bOPV plus 2IPV group), none of which was attributed to the trial intervention. The new vaccination schedule improves immunogenicity against polioviruses, especially against poliovirus type 3. WHO, through a grant from Rotary International (grant number 59735).

Abstract Background Identifying polio vaccine regimens that can elicit robust intestinal mucosal immunity and interrupt viral transmission is a key priority of the polio endgame. Methods In a 2013 Chilean clinical trial (NCT01841671) of trivalent inactivated polio vaccine (IPV) and bivalent oral polio vaccine (bOPV; targeting types 1 and 3), infants were randomized to receive IPV-bOPV-bOPV, IPV-IPV-bOPV, or IPV-IPV-IPV at 8, 16, and 24 weeks of age and challenged with monovalent oral polio vaccine type 2 (mOPV2) at 28 weeks. Using fecal samples collected from 152 participants, we investigated the extent to which IPV-bOPV and IPV-only immunization schedules induced intestinal neutralizing activity and immunoglobulin A against polio types 1 and 2. Results Overall, 37% of infants in the IPV-bOPV groups and 26% in the IPV-only arm had detectable type 2-specific stool neutralization after the primary vaccine series. In contrast, 1 challenge dose of mOPV2 induced brisk intestinal immune responses in all vaccine groups, and significant rises in type 2-specific stool neutralization titers (P < .0001) and immunoglobulin A concentrations (P < 0.0001) were measured 2 weeks after the challenge. In subsidiary analyses, duration of breastfeeding also appeared to be associated with the magnitude of polio-specific mucosal immune parameters measured in infant fecal samples. Conclusions Taken together, these results underscore the concept that mucosal and systemic immune responses to polio are separate in their induction, functionality, and potential impacts on transmission and, specifically, provide evidence that primary vaccine regimens lacking homologous live vaccine components are likely to induce only modest, type-specific intestinal immunity.

Background. The production of Sabin inactivated polio virus vaccine (IPV) can reduce biosafety requirements in the posteradication/post-oral poliovirus vaccine (OPV) era. We conducted a phase II, randomized, positive-controlled trial to assess the safety and immunogenicity of Sabin IPV. Methods. The test groups (A, B, and C) received 3 doses of high, middle, and low D antigen (D Ag) of Sabin IPV at ages 2, 3, and 4 months, respectively. Infants in 2 control groups, group D and group E, received 3 doses of trivalent OPV and conventional IPV (cIPV), respectively, on the same schedule as that of groups A, B, and C. Serum samples were collected before and 30 days after the administration of the third dose. Results. In total, 500 infants were randomly assigned to 5 groups, and 449 infants completed the vaccine series. No serious adverse events were associated with vaccinations. After 3 doses, the seroconversion rates in groups A, B, C, D, and E were 100%, 97.8%, 96.6%, 100%, and 90.1%, respectively, for type 1 poliovirus; 97.7%, 95.7%, 78.7%, 100%, and 90.1%, respectively, for type 2; and 98.8%, 98.9%, 93.3%, 100%, and 97.8%, respectively, for type 3. Conclusions. Sabin IPV has good safety characteristics. The seroconversion rates for type 1 poliovirus (most appropriate concentration, 15 D Ag units [DU]), type 2 (32 DU), and type 3 (45 DU) Sabin IPV were similar to those of the OPV and cIPV control groups. Clinical Trials Registration. NCT01056705.