Serological response and poliovirus excretion following different combined oral and inactivated poliovirus vaccines immunization schedules

Immunogenicity evaluation of primary polio vaccination schedule with inactivated poliovirus vaccines and bivalent oral poliovirus vaccine

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.

Poliovirus type 1 systemic humoral and intestinal mucosal immunity induced by monovalent oral poliovirus vaccine, fractional inactivated poliovirus vaccine, and bivalent oral poliovirus vaccine: A randomized controlled trial

BACKGROUND

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).

METHODS

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).

FINDINGS

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.

INTERPRETATION

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.

FUNDING

U.S. Centers for Disease Control and Prevention.

Challenges and strategies for recruitment of minorities to clinical research and trials

Minority populations are largely absent from clinical research trials. The neglect of these populations has become increasingly apparent, with escalating cancer burdens and chronic disease. The challenges to recruitment of minorities in the United States are multiple including trust or lack thereof. Keys to successful recruitment are responding to community issues, its history, beliefs, and its social and economic pressures. The strategy we have used in many low-income, sometimes remote, communities is to recruit staff from the same community and train them in the required basic research methods. They are the first line of communication. After our arrival in the Texas Rio Grande Valley in 2001, we applied these principles learned over years of global research, to studies of chronic diseases. Beginning in 2004, we recruited and trained a team of local women who enrolled in a cohort of over five thousand Mexican Americans from randomly selected households. This cohort is being followed, and the team has remained, acquiring not only advanced skills (ultrasound, FibroScan, retinal photos, measures of cognition, etc.) but capacity to derive key health information. Currently, we are participating in multiple funded studies, including an NIH clinical trial, liver disease, obesity, and diabetes using multiomics aimed at developing precision medicine approaches to chronic disease prevention and treatment.

Effects of maternal antibodies in infants on the immunogenicity and safety of inactivated polio vaccine in infants

The presence of maternal poliovirus antibodies may interfere with the immune response to inactivated polio vaccine (IPV), and its influence on the safety of vaccination is not yet understood. A total of 1146 eligible infants were randomly assigned (1:1) to the IPV and Sabin IPV (SIPV) groups to compare and analyze the efficacy of the two vaccines in preventing poliovirus infection. We pooled the SIPV and IPV groups and reclassified them into the maternal poliovirus antibody-positive group (MAPG; ≥1: 8) and the maternal poliovirus antibody-negative group (MANG; <1: 8). We evaluated the impact of maternal poliovirus antibodies by comparing the geometric mean titer (GMT), seroconversion rate, and geometric mean increase (GMI) of types I-III poliovirus neutralizing antibodies post-vaccination, and incidence rates of adverse reactions following vaccination between the MAPG and MANG. Respective seroconversion rates in the MAPG and MANG were 94% and 100%, 79.27% and 100%, and 93.26% and 100% (all serotypes, P < .01) for types I-III poliovirus, respectively. The GMT of all types of poliovirus antibodies in the MAPG (1319.13, 219.91, 764.11, respectively) were significantly lower than those in the MANG (1584.92, 286.73, 899.59, respectively) (P < .05). The GMI in the MAPG was significantly lower than that in the MANG (P < .05). No statistically significant difference in the incidence of local and systemic adverse reactions was observed between the MAPG and MANG. Thus, the presence of maternal poliovirus antibodies does not affect the safety of IPV but can negatively impact the immune responses in infants after IPV vaccination.

Review of use of inactivated poliovirus vaccine in campaigns to control type 2 circulating vaccine derived poliovirus (cVDPV) outbreaks

Delivering inactivated poliovirus vaccine (IPV) with oral poliovirus vaccine (OPV) in campaigns has been explored to accelerate the control of type 2 circulating vaccine-derived poliovirus (cVDPV) outbreaks. A review of scientific literature suggests that among populations with high prevalence of OPV failure, a booster with IPV after at least two doses of OPV may close remaining humoral and mucosal immunity gaps more effectively than an additional dose of trivalent OPV. However, IPV alone demonstrates minimal advantage on humoral immunity compared with monovalent and bivalent OPV, and cannot provide the intestinal immunity that prevents infection and spread to those individuals not previously exposed to live poliovirus of the same serotype (i.e. type 2 for children born after the switch from trivalent to bivalent OPV in April 2016). A review of operational data from polio campaigns shows that addition of IPV increases the cost and logistic complexity of campaigns. As a result, campaigns in response to an outbreak often target small areas. Large campaigns require a delay to ensure logistics are in place for IPV delivery, and may need implementation in phases that last several weeks. Challenges to delivery of injectable vaccines through house-to-house visits also increases the risk of missing the children who are more likely to benefit from IPV: those with difficult access to routine immunization and other health services. Based upon this information, the Strategic Advisory Group of Experts in immunization (SAGE) recommended in October 2020 the following strategies: provision of a second dose of IPV in routine immunization to reduce the risk and number of paralytic cases in countries at risk of importation or new emergences; and use of type 2 OPV in high-quality campaigns to interrupt transmission and avoid seeding new type 2 cVDPV outbreaks.

Mucosal immunity to poliovirus

A cornerstone of the global initiative to eradicate polio is the widespread use of live and inactivated poliovirus vaccines in extensive public health campaigns designed to prevent the development of paralytic disease and interrupt transmission of the virus. Central to these efforts is the goal of inducing mucosal immunity able to limit virus replication in the intestine. Recent clinical trials have evaluated new combined regimens of poliovirus vaccines, and demonstrated clear differences in their ability to restrict virus shedding in stool after oral challenge with live virus. Analyses of mucosal immunity accompanying these trials support a critical role for enteric neutralizing IgA in limiting the magnitude and duration of virus shedding. This review summarizes key findings in vaccine-induced intestinal immunity to poliovirus in infants, older children, and adults. The impact of immunization on development and maintenance of protective immunity to poliovirus and the implications for global eradication are discussed.

Immunogenicity of sequential poliovirus vaccination schedules with different strains of poliomyelitis vaccines in Chongqing, China: a cross-sectional survey

A new vaccination schedule with one dose of inactivated polio vaccine (IPV) followed by three doses of bivalent oral attenuated live polio vaccine (bOPV) was introduced in China in 2016. Both Sabin IPV (sIPV) and Salk IPV (wIPV) sequentially with bOPV were accepted in the Chinese routine vaccination schedule. We intended to assess the immunogenicity of the current primary schedule (s/wIPV-bOPV-bOPV) and the schedule in the early stage of the switch (tOPV-bOPV-bOPV), and compare immunogenicity between the groups with different polio virus strains. Healthy infants aged 60–89 days were recruited in hospitals in Chongqing. Infants were assigned to one of three treatments (tOPV-bOPV-bOPV, sIPV-bOPV-bOPV or wIPV-bOPV-bOPV) by enrollment time. Polio neutralizing antibody (NA) assays were conducted to assess immunity. 1027 eligible infants were enrolled. Over 95% seroprotection rates against type I poliovirus (PV1) and type III poliovirus (PV3) were observed in all groups. Infants who received tOPV-bOPV-bOPV had higher antibody titers against type II poliovirus (PV2) than did the IPV-bOPV-bOPV. The geometric mean titers (GMTs) of PV2 were only ~20 in the IPV-bOPV-bOPV. GMTs of PV1 were higher than PV3 in s/wIPV-bOPV-bOPV. The primary schedule of s/wIPV-bOPV-bOPV is insufficient to protect children against PV2, and the NA titer to PV3 is lower. Higher antibody responses were induced in sIPV-bOPV-bOPV than that in wIPV-bOPV-bOPV. Supplementary vaccination with one dose of IPV is necessary for children who had no tOPV immune history or had only one IPV to induce higher levels of immunity against PV2 and PV3.

Randomized Controlled Clinical Trial of bivalent Oral Poliovirus Vaccine and Inactivated Poliovirus Vaccine in Nigerian Children

BACKGROUND

We conducted a trial in Nigeria to assess the immunogenicity of the new bOPV + IPV immunization schedule and gains in type 2 immunity with addition of second dose of IPV. The trial was conducted in August 2016-March 2017 period, well past the tOPV-bOPV switch in April 2016.

METHODS

This was an open-label, two-arm, non-inferiority, multi-center, randomized controlled trial. We enrolled 572 infants of age ≤14 days and randomized them into two arms. Arm A received bOPV at birth, 6 and 10 weeks, bOPV+IPV at week 14 and IPV at week 18. Arm B received IPV each at 6, 10, 14 weeks and bOPV at 18 weeks of age.

RESULTS

Seroconversion rates for poliovirus types 1 and 3, respectively, were 98.9% (95%CI:96.7-99.8) and 98.1% (95%CI:88.2-94.8) in Arm A, and 89.6% (95%CI:85.4-93.0) and 98.5% (95%CI:96.3-99.6) in Arm B. Type 2 seroconversion with one dose IPV in Arm A was 72.0% (95%CI:66.2-77.3), which increased significantly with addition of second dose to 95.9% (95%CI:92.8-97.9).

CONCLUSION

This first trial on the new EPI schedule in a sub-Saharan African country demonstrated excellent immunogenicity against poliovirus types 1 and 3, and substantial/enhanced immunogenicity against poliovirus type 2 after 1 to 2 doses of IPV respectively.

Impact of Maternal Antibody on the Immunogenicity of Inactivated Polio Vaccine in Infants Immunized With Bivalent Oral Polio Vaccine: Implications for the Polio Eradication Endgame

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.

Immunogenicity of type 2 monovalent oral and inactivated poliovirus vaccines for type 2 poliovirus outbreak response: an open-label, randomised controlled trial

BACKGROUND

Monovalent type 2 oral poliovirus vaccine (mOPV2) and inactivated poliovirus vaccine (IPV) are used to respond to type 2 poliovirus outbreaks. We aimed to assess the effect of two mOPV2 doses on the type 2 immune response by varying the time interval between mOPV2 doses and IPV co-administration with mOPV2.

METHODS

We did a randomised, controlled, parallel, open-label, non-inferiority, inequality trial at two study clinics in Dhaka, Bangladesh. Healthy infants aged 6 weeks (42-48 days) at enrolment were randomly assigned (1:1:1:1) to receive two mOPV2 doses (each dose consisting of two drops [0·1 mL in total] of about 105 50% cell culture infectious dose of type 2 Sabin strain) at intervals of 1 week, 2 weeks, 4 weeks (standard or control group), or 4 weeks with IPV (0·5 mL of type 1 [Mahoney, 40 D-antigen units], type 2 [MEF-1, 8 D-antigen units], and type 3 [Saukett, 32 D-antigen units]) administered intramuscularly with the first mOPV2 dose. We used block randomisation, randomly selecting blocks of sizes four, eight, 12, or 16 stratified by study sites. We concealed randomisation assignment from staff managing participants in opaque, sequentially numbered, sealed envelopes. Parents and clinic staff were unmasked to assignment after the randomisation envelope was opened. Laboratory staff analysing sera were masked to assignment, but investigators analysing data and assessing outcomes were not. The primary outcome was type 2 immune response measured 4 weeks after mOPV2 administration. The primary modified intention-to-treat analysis included participants with testable serum samples before and after vaccination. A non-inferiority margin of 10% and p=0·05 (one-tailed) was used. This trial is registered at ClinicalTrials.gov, number NCT02643368, and is closed to accrual.

FINDINGS

Between Dec 7, 2015, and Jan 5, 2016, we randomly assigned 760 infants to receive two mOPV2 doses at intervals of 1 week (n=191), 2 weeks (n=191), 4 weeks (n=188), or 4 weeks plus IPV (n=190). Immune responses after two mOPV2 doses were observed in 161 (93%) of 173 infants with testable serum samples in the 1 week group, 169 (96%) of 177 in the 2 week group, and 176 (97%) of 181 in the 4 week group. 1 week and 2 week intervals between two mOPV2 doses were non-inferior to 4 week intervals because the lower bound of the absolute differences in the percentage of immune responses were greater than -10% (-4·2% [90% CI -7·9 to -0·4] in the 1 week group and -1·8% [-5·0 to 1·5] in the 2 week group vs the 4 week group). The immune response elicited by two mOPV2 doses 4 weeks apart was not different when IPV was added to the first dose (176 [97%] of 182 infants with IPV vs 176 [97%] of 181 without IPV; p=1·0). During the trial, two serious adverse events (pneumonia; one [1%] of 186 patients in the 1 week group and one [1%] of 182 in the 4 week group) and no deaths were reported; the adverse events were not attributed to the vaccines.

INTERPRETATION

Administration of mOPV2 at short intervals does not interfere with its immunogenicity. The addition of IPV to the first mOPV2 dose did not improve poliovirus type 2 immune response.

FUNDING

US Centers for Disease Control and Prevention.

Effect of substituting IPV for tOPV on immunity to poliovirus in Bangladeshi infants: An open-label randomized controlled trial

BACKGROUND

The Polio Endgame strategy includes phased withdrawal of oral poliovirus vaccines (OPV) coordinated with introduction of inactivated poliovirus vaccine (IPV) to ensure population immunity. The impact of IPV introduction into a primary OPV series of immunizations in a developing country is uncertain.

METHODS

Between May 2011 and November 2012, we enrolled 700 Bangladeshi infant-mother dyads from Dhaka slums into an open-label randomized controlled trial to test whether substituting an injected IPV dose for the standard Expanded Program on Immunization (EPI) fourth tOPV dose at infant age 39 weeks would reduce fecal shedding and enhance systemic immunity. The primary endpoint was mucosal immunity to poliovirus at age one year, measured by fecal excretion of any Sabin virus at five time points up to 25 days post-52 week tOPV challenge, analyzed by the intention to treat principle.

FINDINGS

We randomized 350 families to the tOPV and IPV vaccination arms. Neither study arm resulted in superior intestinal protection at 52 weeks measured by the prevalence of infants shedding any of three poliovirus serotypes, but the IPV dose induced significantly higher seroprevalence and seroconversion rates. This result was identical for poliovirus detection by cell culture or RT-qPCR. The non-significant estimated culture-based shedding risk difference was -3% favoring IPV, and the two vaccination schedules were inferred to be equivalent within a 95% confidence margin of -10% to +4%. Results for shedding analyses stratified by poliovirus type were similar.

CONCLUSIONS

Neither of the vaccination regimens is superior to the other in enhancing intestinal immunity as measured by poliovirus shedding at 52 weeks of age and the IPV regimen provides similar intestinal immunity to the four tOPV series, although the IPV regimen strongly enhances humoral immunity. The IPV-modified regimen may be considered for vaccination programs without loss of intestinal protection.

Impact of inactivated poliovirus vaccine on mucosal immunity: implications for the polio eradication endgame

The polio eradication endgame aims to bring transmission of all polioviruses to a halt. To achieve this aim, it is essential to block viral replication in individuals via induction of a robust mucosal immune response. Although it has long been recognized that inactivated poliovirus vaccine (IPV) is incapable of inducing a strong mucosal response on its own, it has recently become clear that IPV may boost immunity in the intestinal mucosa among individuals previously immunized with oral poliovirus vaccine. Indeed, mucosal protection appears to be stronger following a booster dose of IPV than oral poliovirus vaccine, especially in older children. Here, we review the available evidence regarding the impact of IPV on mucosal immunity, and consider the implications of this evidence for the polio eradication endgame. We conclude that the implementation of IPV in both routine and supplementary immunization activities has the potential to play a key role in halting poliovirus transmission, and thereby hasten the eradication of polio.

Monovalent type-1 oral poliovirus vaccine given at short intervals in Pakistan: a randomised controlled, four-arm, open-label, non-inferiority trial

BACKGROUND

Supplementary immunisation activities with oral poliovirus vaccines (OPVs) are usually separated by 4 week intervals; however, shorter intervals have been used in security-compromised areas and for rapid outbreak responses. We assessed the immunogenicity of monovalent type-1 oral poliovirus vaccine (mOPV1) given at shorter than usual intervals in Karachi, Pakistan.

METHODS

This was a multicentre, randomised, controlled, four-arm, open-label, non-inferiority trial done at five primary health-care centres in low-income communities in and around Karachi, Pakistan. Eligible participants were healthy newborn babies with a birthweight of at least 2·5 kg, for whom informed consent was provided by their parent or guardian, and lived less than 30 km from the study clinic. After receiving a birth dose of trivalent OPV, we enrolled and randomly assigned newborn babies (1:1:1:1) to receive two doses of mOPV1 with an interval of 1 week (mOPV1-1 week), 2 weeks (mOPV1-2 weeks), or 4 weeks (mOPV1-4 weeks) between doses, or two doses of bivalent OPV (bOPV) with an interval of 4 weeks between doses (bOPV-4 weeks). We gave the first study dose of OPV at age 6 weeks. We did the randomisation with a centrally generated, computerised allocation sequence with blocks of 16; participants' families and study physicians could not feasibly be masked to the allocations. Trial participants were excluded from local supplementary immunisation activities during the study period. The primary outcome was non-inferiority (within a 20% margin) between groups in seroconversion to type-1 poliovirus. The primary and safety analyses were done in the per-protocol population of infants who received all three doses of vaccine. This trial is registered with ClinicalTrials.gov, number NCT01586572, and is closed to new participants.

FINDINGS

Between March 1, 2012, and May 31, 2013, we enrolled 1009 newborn babies, and randomly assigned 829 (82%) to treatment. 554 (67%) of the 829 babies were included in the per-protocol analysis. Proportions of seroconversion to type-1 poliovirus were 107/135 (79%, 95% CI 72·4-86·1) with mOPV1-1 week, 108/135 (80%, 73·2-86·8) with mOPV1-2 weeks, 129/148 (87%, 80·9-92·0) with mOPV1-4 weeks, and 107/136 (79%, 71·8-85·6) with bOPV-4 weeks. Non-inferiority was shown between groups and no significant differences were noted. Ten participants died during the trial. Seven of these deaths occurred during the lead-in period before randomisation (two from diarrhoea, five from unknown causes). Three infants died from sepsis after random assignment. No deaths were attributed to the procedures or vaccines. Additionally, we noted no events of vaccine-associated paralysis.

INTERPRETATION

We identified no significant differences in responses to mOPV1 given with shorter intervals between doses than with the standard 4 week intervals. The short-interval strategy could be particularly beneficial when temporary windows of opportunity for safe access can be granted in areas of conflict--eg, during cease-fire periods. In such situations, we recommend shortening the interval between OPV doses to 7 days.

FUNDING

World Health Organization.

Polio vaccination: past, present and future

Live attenuated oral polio vaccine (OPV) and inactivated polio vaccine (IPV) are the tools being used to achieve eradication of wild polio virus. Because OPV can rarely cause paralysis and generate revertant polio strains, IPV will have to replace OPV after eradication of wild polio virus is certified to sustain eradication of all polioviruses. However, uncertainties remain related to IPV's ability to induce intestinal immunity in populations where fecal-oral transmission is predominant. Although substantial effectiveness and safety data exist on the use and delivery of OPV and IPV, several new research initiatives are currently underway to fill specific knowledge gaps to inform future vaccination policies that would assure polio is eradicated and eradication is maintained.

Effect of a single inactivated poliovirus vaccine dose on intestinal immunity against poliovirus in children previously given oral vaccine: an open-label, randomised controlled trial

BACKGROUND

Intestinal immunity induced by oral poliovirus vaccine (OPV) is imperfect and wanes with time, permitting transmission of infection by immunised children. Inactivated poliovirus vaccine (IPV) does not induce an intestinal mucosal immune response, but could boost protection in children who are mucosally primed through previous exposure to OPV. We aimed to assess the effect of IPV on intestinal immunity in children previously vaccinated with OPV.

METHODS

We did an open-label, randomised controlled trial in children aged 1-4 years from Chinnallapuram, Vellore, India, who were healthy, had not received IPV before, and had had their last dose of OPV at least 6 months before enrolment. Children were randomly assigned (1:1) to receive 0·5 mL IPV intramuscularly (containing 40, 8, and 32 D antigen units for serotypes 1, 2, and 3) or no vaccine. The randomisation sequence was computer generated with a blocked randomisation procedure with block sizes of ten by an independent statistician. The laboratory staff did blinded assessments. The primary outcome was the proportion of children shedding poliovirus 7 days after a challenge dose of serotype 1 and 3 bivalent OPV (bOPV). A second dose of bOPV was given to children in the no vaccine group to assess intestinal immunity resulting from the first dose. A per-protocol analysis was planned for all children who provided a stool sample at 7 days after bOPV challenge. This trial is registered with Clinical Trials Registry of India, number CTRI/2012/09/003005.

FINDINGS

Between Aug 19, 2013, and Sept 13, 2013, 450 children were enrolled and randomly assigned into study groups. 225 children received IPV and 225 no vaccine. 222 children in the no vaccine group and 224 children in the IPV group had stool samples available for primary analysis 7 days after bOPV challenge. In the IPV group, 27 (12%) children shed serotype 1 poliovirus and 17 (8%) shed serotype 3 poliovirus compared with 43 (19%) and 57 (26%) in the no vaccine group (risk ratio 0·62, 95% CI 0·40-0·97, p=0·0375; 0·30, 0·18-0·49, p<0·0001). No adverse events were related to the study interventions.

INTERPRETATION

The substantial boost in intestinal immunity conferred by a supplementary dose of IPV given to children younger than 5 years who had previously received OPV shows a potential role for this vaccine in immunisation activities to accelerate eradication and prevent outbreaks of poliomyelitis.

FUNDING

Bill & Melinda Gates Foundation.

Polio eradication. Efficacy of inactivated poliovirus vaccine in India

Inactivated poliovirus vaccine (IPV) is efficacious against paralytic disease, but its effect on mucosal immunity is debated. We assessed the efficacy of IPV in boosting mucosal immunity. Participants received IPV, bivalent 1 and 3 oral poliovirus vaccine (bOPV), or no vaccine. A bOPV challenge was administered 4 weeks later, and excretion was assessed 3, 7, and 14 days later. Nine hundred and fifty-four participants completed the study. Any fecal shedding of poliovirus type 1 was 8.8, 9.1, and 13.5% in the IPV group and 14.4, 24.1, and 52.4% in the control group by 6- to 11-month, 5-year, and 10-year groups, respectively (IPV versus control: Fisher's exact test P < 0.001). IPV reduced excretion for poliovirus types 1 and 3 between 38.9 and 74.2% and 52.8 and 75.7%, respectively. Thus, IPV in OPV-vaccinated individuals boosts intestinal mucosal immunity.

National choices related to inactivated poliovirus vaccine, innovation and the endgame of global polio eradication

Achieving the goal of a world free of poliomyelitis still requires significant effort. Although polio immunization represents a mature area, the polio endgame will require new tools and strategies, particularly as national and global health leaders coordinate the cessation of all three serotypes of oral poliovirus vaccine and increasingly adopt inactivated poliovirus vaccine (IPV). Poliovirus epidemiology and the global options for managing polioviruses continue to evolve, along with our understanding and appreciation of the resources needed and the risks that require management. Based on insights from modeling, we offer some perspective on the current status of plans and opportunities to achieve and maintain a world free of wild polioviruses and to successfully implement oral poliovirus vaccine cessation. IPV costs and potential wastage will represent an important consideration for national policy makers. Innovations may reduce future IPV costs, but the world urgently needs lower-cost IPV options.

A quantitative survey of the literature on poliovirus infection and immunity

OBJECTIVE

To examine forces that drive vaccination policy to eradicate wild- and vaccine-derived poliovirus, and to focus on the efficacy of vaccines to support decision-making and further research.

METHODS

We searched PubMed and Ovid databases for English-language publications, without date restrictions. We also collected references from major reviews on polio vaccine immunogenicity or protection. We conducted a meta-analysis of human immunity to polio infections using multiple non-linear regression, and built a database from a broad (but not systematic) set of polio vaccine studies (46 studies, >10000 subjects).

RESULTS

The outcome was an immunological model representative of many different datasets. Parameters measured immunogenicity to both humoral and mucosal immune compartments for Salk and Sabin vaccines. The immunity model was more highly correlated with the data than a simpler per-dose efficacy model.

CONCLUSIONS

The model offers new insights for immunization policy. We measured the mucosal immunogenicity of IPV to a precision that is useful in decision-making for end-game polio immunization policies.

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.

Preeradication vaccine policy options for poliovirus infection and disease control

With the circulation of wild poliovirus (WPV) types 1 and 3 continuing more than a decade after the original goal of eradicating all three types of WPVs by 2000, policymakers consider many immunization options as they strive to stop transmission in the remaining endemic and outbreak areas and prevent reintroductions of live polioviruses into nonendemic areas. While polio vaccination choices may appear simple, our analysis of current options shows remarkable complexity. We offer important context for current and future polio vaccine decisions and policy analyses by developing decision trees that clearly identify potential options currently used by countries as they evaluate national polio vaccine choices. Based on a comprehensive review of the literature we (1) identify the current vaccination options that national health leaders consider for polio vaccination, (2) characterize current practices and factors that appear to influence national and international choices, and (3) assess the evidence of vaccine effectiveness considering sources of variability between countries and uncertainties associated with limitations of the data. With low numbers of cases occurring globally, the management of polio risks might seem like a relatively low priority, but stopping live poliovirus circulation requires making proactive and intentional choices to manage population immunity in the remaining endemic areas and to prevent reestablishment in nonendemic areas. Our analysis shows remarkable variability in the current national polio vaccine product choices and schedules, with combination vaccine options containing inactivated poliovirus vaccine and different formulations of oral poliovirus vaccine making choices increasingly difficult for national health leaders.

Expert review on poliovirus immunity and transmission

Successfully managing risks to achieve wild polioviruses (WPVs) eradication and address the complexities of oral poliovirus vaccine (OPV) cessation to stop all cases of paralytic poliomyelitis depends strongly on our collective understanding of poliovirus immunity and transmission. With increased shifting from OPV to inactivated poliovirus vaccine (IPV), numerous risk management choices motivate the need to understand the tradeoffs and uncertainties and to develop models to help inform decisions. The U.S. Centers for Disease Control and Prevention hosted a meeting of international experts in April 2010 to review the available literature relevant to poliovirus immunity and transmission. This expert review evaluates 66 OPV challenge studies and other evidence to support the development of quantitative models of poliovirus transmission and potential outbreaks. This review focuses on characterization of immunity as a function of exposure history in terms of susceptibility to excretion, duration of excretion, and concentration of excreted virus. We also discuss the evidence of waning of host immunity to poliovirus transmission, the relationship between the concentration of poliovirus excreted and infectiousness, the importance of different transmission routes, and the differences in transmissibility between OPV and WPV. We discuss the limitations of the available evidence for use in polio risk models, and conclude that despite the relatively large number of studies on immunity, very limited data exist to directly support quantification of model inputs related to transmission. Given the limitations in the evidence, we identify the need for expert input to derive quantitative model inputs from the existing data.

Oral and inactivated poliovirus vaccines in the newborn: a review

BACKGROUND

Oral poliovirus vaccine (OPV) remains the vaccine-of-choice for routine immunization and supplemental immunization activities (SIAs) to eradicate poliomyelitis globally. Recent data from India suggested lower than expected immunogenicity of an OPV birth dose, prompting a review of the immunogenicity of OPV or inactivated poliovirus vaccine (IPV) when administered at birth.

METHODS

We evaluated the seroconversion and reported adverse events among infants given a single birth dose (given ≤7 days of life) of OPV or IPV through a systematic review of published articles and conference abstracts from 1959 to 2011 in any language found on PubMed, Google Scholar, or reference lists of selected articles.

RESULTS

25 articles from 13 countries published between 1959 and 2011 documented seroconversion rates in newborns following an OPV dose given within the first seven days of life. There were 10 studies that measured seroconversion rates between 4 and 8 weeks of a single birth dose of TOPV, using an umbilical cord blood draw at the time of birth to establish baseline antibody levels. The percentage of newborns who seroconverted at 8 weeks range from 6-42% for poliovirus type 1, 2-63% for type 2, and 1-35% for type 3. For mOPV type 1, seroconversion ranged from 10 to 76%; mOPV type 3, the range was 12-58%; and for the one study reporting bOPV, it was 20% for type 1 and 7% for type 3. There were four studies of IPV in newborns with a seroconversion rate of 8-100% for serotype 1, 15-100% for serotype 2, and 15-94% for serotype 3, measured at 4-6 weeks of life. No serious adverse events related to newborn OPV or IPV dosing were reported, including no cases of acute flaccid paralysis.

CONCLUSIONS

There is great variability of the immunogenicity of a birth dose of OPV for reasons largely unknown. Our review confirms the utility of a birth dose of OPV, particularly in countries where early induction of polio immunity is imperative. IPV has higher seroconversion rates in newborns and may be a superior choice in countries which can afford IPV, but there have been few studies of an IPV dose for newborns.

Systematic review of mucosal immunity induced by oral and inactivated poliovirus vaccines against virus shedding following oral poliovirus challenge

Inactivated poliovirus vaccine (IPV) may be used in mass vaccination campaigns during the final stages of polio eradication. It is also likely to be adopted by many countries following the coordinated global cessation of vaccination with oral poliovirus vaccine (OPV) after eradication. The success of IPV in the control of poliomyelitis outbreaks will depend on the degree of nasopharyngeal and intestinal mucosal immunity induced against poliovirus infection. We performed a systematic review of studies published through May 2011 that recorded the prevalence of poliovirus shedding in stool samples or nasopharyngeal secretions collected 5-30 days after a "challenge" dose of OPV. Studies were combined in a meta-analysis of the odds of shedding among children vaccinated according to IPV, OPV, and combination schedules. We identified 31 studies of shedding in stool and four in nasopharyngeal samples that met the inclusion criteria. Individuals vaccinated with OPV were protected against infection and shedding of poliovirus in stool samples collected after challenge compared with unvaccinated individuals (summary odds ratio [OR] for shedding 0.13 (95% confidence interval [CI] 0.08-0.24)). In contrast, IPV provided no protection against shedding compared with unvaccinated individuals (summary OR 0.81 [95% CI 0.59-1.11]) or when given in addition to OPV, compared with individuals given OPV alone (summary OR 1.14 [95% CI 0.82-1.58]). There were insufficient studies of nasopharyngeal shedding to draw a conclusion. IPV does not induce sufficient intestinal mucosal immunity to reduce the prevalence of fecal poliovirus shedding after challenge, although there was some evidence that it can reduce the quantity of virus shed. The impact of IPV on poliovirus transmission in countries where fecal-oral spread is common is unknown but is likely to be limited compared with OPV.

Waning intestinal immunity after vaccination with oral poliovirus vaccines in India

BACKGROUND

The eradication of wild-type polioviruses in areas with efficient fecal-oral transmission relies on intestinal mucosal immunity induced by oral poliovirus vaccine (OPV). Mucosal immunity is thought to wane over time but the rate of loss of protection has not been examined.

METHODS

We examined the degree and duration of intestinal mucosal immunity in India by measuring the prevalence of vaccine poliovirus in stool samples collected 4-28 days after a "challenge" dose of OPV among 47 574 children with acute flaccid paralysis reported during 2005-2009.

RESULTS

Previous vaccination with OPV was protective against excretion of vaccine poliovirus after challenge, but the odds of excretion increased significantly with the time since the child was last exposed to an immunization activity (odds ratio, 1.39 [95% confidence interval .99-1.97], 2.04 [1.28-3.25], and 1.31 [1.00-1.70] comparing ≥6 months with 1 month ago for serotypes 1, 2, and 3, respectively). Vaccine administered during the high season for enterovirus infections (April-September) was significantly less likely to result in excretion, especially in northern states (odds ratio, 0.57 [95% confidence interval, .50-.65], 0.58 [.41-.81], and 0.48 [.40-.57] for serotypes 1, 2, and 3).

CONCLUSIONS

Infection with OPV (vaccine "take") is highly seasonal in India and results in intestinal mucosal immunity that appears to wane significantly within a year of vaccination.

Oral polio vaccines and their role in polio eradication in India

Although the oral polio vaccine has reduced the incidence of polio in India, the current polio scenario indicates that oral polio vaccine cannot eradicate polio from Uttar Pradesh and Bihar, two states that have approximately 32% of the total Indian population and report more than 96% of polio cases that occur in India. Poor response to oral polio vaccine by some children from these two states could be due to genetic factors. Thus, for polio eradication in India, inactivated polio vaccine is needed.

Shedding and reversion of oral polio vaccine type 3 in Mexican vaccinees: comparison of mutant analysis by PCR and enzyme cleavage to a real-time PCR assay

A uracil-to-cytosine mutation at nucleotide position 472 of oral poliovirus vaccine type 3 (OPV3) contributes to the development of vaccine-associated paralytic poliomyelitis (VAPP). To analyze OPV3 shedding patterns, we previously used the multistep method of mutant analysis by PCR and enzyme cleavage (MAPREC). This involves conventional reverse transcription-PCR to detect OPV3, followed by a restriction digest to quantify position 472 reversion. Real-time PCR detects and quantifies nucleic acid as PCR occurs and avoids postreaction processing. The goal of this study was to compare a real-time PCR method to MAPREC. Seventy-three stool samples from Mexican OPV recipients underwent the reverse transcription-PCR step of MAPREC and real-time PCR. Real-time PCR identified 23% more OPV3-positive samples than conventional reverse transcription-PCR. When reversion was compared, the revertant proportion (RP), defined as the percentage of revertants in a sample, differed by < or =10% in 21/25 (84%) samples. The four samples differing by >10% were obtained within 5 days of OPV administration. The real-time PCR assay identified samples with an RP of > or =85% with 94% sensitivity and 86% specificity compared to MAPREC. The mean difference in RP between the two methods was 3.6% (95% confidence interval, -0.3 to 7.5%). Real-time PCR methods reliably detect OPV3, and reversion estimates correlate more consistently with MAPREC when OPV3 reversion rates are high. Detecting VAPP-related mutations by real-time PCR is rapid and efficient and can be useful in monitoring ongoing global polio eradication efforts.

Randomized, placebo-controlled trial of inactivated poliovirus vaccine in Cuba

BACKGROUND

After poliomyelitis has been eradicated, access to live polioviruses will be highly restricted and the use of oral poliovirus vaccine (OPV) will probably be discontinued. Countries using OPV must decide whether to switch to inactivated poliovirus vaccine (IPV) or stop polio vaccination. Because data on the immunogenicity of IPV in tropical developing countries are limited, we conducted a randomized, controlled trial of IPV in Cuba.

METHODS

The study population consisted of healthy infants born in Havana. A total of 166 infants were randomly assigned to two groups. Group A received a combination of the diphtheria-pertussis-tetanus (DPT) vaccine, the Haemophilus influenzae type b (Hib) vaccine, and IPV (DPT-Hib-IPV) at 6, 10, and 14 weeks of age. Group B, the control group, received a combination of the DPT vaccine and the Hib vaccine at 6, 10, and 14 weeks of age. Another group (group C, 100 infants), which did not undergo randomization at the same time as groups A and B, received the DPT-Hib-IPV combination at 8 and 16 weeks of age. Serum samples were collected before vaccination and at least 4 weeks after the last dose. Stool samples were obtained before and 7 days after challenge with OPV.

RESULTS

The seroconversion rates in group A were 94%, 83%, and 100% for types 1, 2, and 3 poliovirus, respectively. There were no seroconversions in group B. The seroconversion rates in group C were 90%, 89%, and 90% for poliovirus types 1, 2, and 3, respectively. For groups A, B, and C, the virus isolation rates after challenge with OPV were 94%, 91%, and 97%, respectively, and the mean log10 viral titers of any serotype were 3.46, 3.89, and 3.37, respectively. There was one major adverse event, an episode of hypotonia.

CONCLUSIONS

Vaccination with two or three doses of IPV resulted in a rate of seroconversion of at least 90%, except for seroconversion against type 2. The viral titer of OPV shed in the stool after OPV challenge was reduced in both groups receiving IPV. (ClinicalTrials.gov number, NCT00260312 [ClinicalTrials.gov].).

Controversies in polio immunization

Vaccines against poliomyelitis have been in use for nearly five decades now and have played a major role in progress towards global eradication of the disease. Both the vaccines, (oral polio vaccine and inactivated polio vaccine) and their uses are still debated with particular reference to their selective advantages vs. disadvantages, choice for individual vs. community protection and their administration strategies. Further occurrence of vaccine associated paralytic poliomyelitis with oral vaccine assumes importance in the face of disappearing disease. Further availability of inactivated polio vaccine in India and its various schedules such as sequential and combination schedules show some promise for polio eradication.