Boosting of Mucosal Immunity After Fractional-Dose Inactivated Poliovirus Vaccine

Global Disparities in Access to Vaccine Clinical Trials: A Review of the Literature

Vaccines are an effective tool to reduce the disease burden from infectious diseases on a population, infrastructural, and individual level. Before vaccines can be administered to populations at large, they must go through rigorous testing in the form of clinical trials. While vaccine trials can be used to assess the efficacy of interventions on a local populace as well as target local endemic diseases, most clinical trials are sponsored and conducted by companies in high-income countries (HICs). This can lead to vaccines that are not optimized for low- and middle-income countries (LMICs) and that often neglect to address diseases specific to the local population. This narrative review aims to explore the factors leading to discrepancies in the execution of and access to vaccine trials between HICs and LMICs, thus guiding future efforts in confronting them. This review was written using the literature sourced from the PubMed database and supplemented with articles from Google Scholar along with grey literature. Several themes are highlighted including poorly defined regulatory and ethical guidelines, staff shortages, lack of research infrastructure, and logistical barriers. We discuss how these challenges have affected vaccine development in various capacities through case examples of SARS-CoV-2, poliovirus, and malaria. Many challenges remain in equitable vaccine clinical trial development and implementation. Facilitating the implementation of locally sponsored vaccine clinical trials in LMICs may be one avenue to address these challenges. In doing so, LMICs can become active stakeholders in the health of their citizens by addressing endemic diseases, tailoring vaccine specifications based on local needs, and implementing wide-scale vaccine access and delivery.

Impact of Supplementary Immunization Activities using Novel Oral Polio Vaccine Type 2 during a Large outbreak of Circulating Vaccine-Derived Poliovirus in Nigeria

BACKGROUND

Novel oral poliovirus vaccine (OPV) type 2 (nOPV2) has been made available for outbreak response under an emergency use listing authorization based on supportive clinical trial data. Since 2021 more than 350 million doses of nOPV2 were used for control of a large outbreak of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Nigeria.

METHODS

Using a bayesian time-series susceptible-infectious-recovered model, we evaluate the field effectiveness of nOPV2 immunization campaigns in Nigeria compared with campaigns using monovalent OPV type 2 (mOPV2).

RESULTS

We found that both nOPV2 and mOPV2 campaigns were highly effective in reducing transmission of cVDPV2, on average reducing the susceptible population by 42% (95% confidence interval, 28-54%) and 38% (20-51%) per campaign, respectively, which were indistinguishable from each other in this analysis (relative effect, 1.1 [.7-1.9]). Impact was found to vary across areas and between immunization campaigns.

CONCLUSIONS

These results are consistent with the comparable individual immunogenicity of nOPV2 and mOPV2 found in clinical trials but also suggest that outbreak response campaigns may have small impacts in some areas requiring more campaigns than are suggested in current outbreak response procedures.

Mucosal immunity to poliovirus in children 0-15 years of age: A community-based study in Karachi, Pakistan in 2019

This study assesses poliovirus type 1 (PV1) immunity in children to inform the contribution of mucosal immunity in and preventing poliovirus circulation. A community-based study was conducted in peri-urban Karachi, Pakistan. Randomly selected children (0-15 years) received oral poliovirus vaccine (OPV) challenge dose. Blood and stool samples were collected at several time points and evaluated for polio-neutralizing antibodies and serotype-specific poliovirus, respectively. 81/589 (14%) children excreted PV1 7 days post-OPV-challenge; 70/81 (86%) were seropositive at baseline. 12/610 (2%) were asymptomatic Wild Poliovirus Type 1 (WPV1) excretors. Most poliovirus excretors had humoral immunity, suggesting mucosal immunity in these children likely waned or never developed. Without mucosal immunity, they are susceptible to poliovirus infection, shedding, and transmission. Asymptomatic WPV1 excretion suggests undetected poliovirus circulation within the community.

Does IPV Boost Intestinal Immunity among Children under Five Years of Age? An Experience from Pakistan

The oral poliovirus vaccine (OPV) has been the mainstay of polio eradication, especially in low-income countries, and its use has eliminated wild poliovirus type 2. However, the inactivated poliovirus vaccine (IPV) is safer than OPV, as IPV protects against paralytic poliomyelitis without producing adverse reactions. The present study compared mucosal and humoral responses to poliovirus vaccines administered to previously OPV-immunized children to assess the immunity gap in children in areas of high poliovirus transmission. A cluster-randomized trial was implemented in three high-risk districts of Pakistan-Karachi, Kashmore, and Bajaur-from June 2013 to May 2014. This trial was community-oriented and included three arms, focusing on healthy children below five years of age. The study involved the randomization of 387 clusters, of which 360 were included in the final analysis. The control arm (A) received the routine polio program bivalent poliovirus vaccine (bOPV). The second arm (B) received additional interventions, including health camps providing routine vaccinations and preventive maternal and child health services. In addition to the interventions in arm B, the third arm (C) was also provided with IPV. Blood and stool samples were gathered from children to evaluate humoral and intestinal immunity. The highest levels of poliovirus type 1 serum antibodies were observed in Group C (IPV + OPV). The titers for poliovirus type 2 (P2) and poliovirus type 3 (P3) were noticeably higher in those who had received a routine OPV dose than in those who had not across all study groups and visits. Providing an IPV booster after at least two OPV doses could potentially fill immunity gaps in regions where OPV does not show high efficacy. However, IPV only marginally enhances humoral immunity and fails to offer intestinal immunity, which is critical to stop the infection and spread of live poliovirus in populations that have not been exposed before.

Intradermal fractional-dose inactivated polio vaccine (fIPV) adjuvanted with double mutant Enterotoxigenic Escherichia coli heat labile toxin (dmLT) is well-tolerated and augments a systemic immune response to all three poliovirus serotypes in a randomized placebo-controlled trial

Eradication of poliomyelitis globally is constrained by fecal shedding of live polioviruses, both wild-type and vaccine-derived strains, into the environment. Although inactivated polio vaccines (IPV) effectively protect the recipient from clinical poliomyelitis, fecal shedding of live virus still occurs following infection with either wildtype or vaccine-derived strains of poliovirus. In the drive to eliminate the last cases of polio globally, improvements in both oral polio vaccines (OPV) (to prevent reversion to virulence) and injectable polio vaccines (to improve mucosal immunity and prevent viral shedding) are underway. The E. coli labile toxin with two or "double" attenuating mutations (dmLT) may boost immunologic responses to IPV, including at mucosal sites. We performed a double-blinded phase I controlled clinical trial to evaluate safety, tolerability, as well as systemic and mucosal immunogenicity of IPV adjuvanted with dmLT, given as a fractional (1/5th) dose intradermally (fIPV-dmLT). Twenty-nine volunteers with no past exposure to OPV were randomized to a single dose of fIPV-dmLT or fIPV alone. fIPV-dmLT was well tolerated, although three subjects had mild but persistent induration and hyperpigmentation at the injection site. A ≥ 4-fold rise in serotype-specific neutralizing antibody (SNA) titers to all three serotypes was seen in 84% of subjects receiving fIPV-dmLT vs. 50% of volunteers receiving IPV alone. SNA titers were higher in the dmLT-adjuvanted group, but only differences in serotype 1 were significant. Mucosal immune responses, as measured by polio serotype specific fecal IgA were minimal in both groups and differences were not seen. fIPV-dmLT may offer a benefit over IPV alone. Beyond NAB responses protecting the individual, studies demonstrating the ability of fIPV-dmLT to prevent viral shedding are necessary. Studies employing controlled human infection models, using monovalent OPV post-vaccine are ongoing. Studies specifically in children may also be necessary and additional biomarkers of mucosal immune responses in this population are needed. Clinicaltrials.gov Identifer: NCT03922061.

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.

Intradermal administration of fractional doses of the inactivated poliovirus vaccine in a campaign: a pragmatic, open-label, non-inferiority trial in The Gambia

BACKGROUND

A rapid increase in circulating vaccine-derived poliovirus type 2 outbreaks, and the need to reserve inactivated poliovirus vaccine (IPV) for routine immunisation, has increased the value of fractional dose IPV (fIPV) as a measure to prevent acute flaccid paralysis. However, the intradermal route of administration has been viewed as prohibitive to outbreak response campaigns. We aimed to establish the immunogenicity and safety of administering intradermal fIPV with a disposable syringe jet injector (DSJI) or an intradermal adaptor (IDA) compared with standard administration with a BCG needle and syringe (N&S).

METHODS

This pragmatic, non-inferiority trial was undertaken in a campaign setting in communities in The Gambia. Children aged 4-59 months without contraindication to vaccination were eligible. Children were not individually randomly assigned; instead, the vaccination teams were randomly assigned (1:1:1) to one of three administration methods. Parents and the field team were not masked, but laboratory personnel were masked. Baseline demographic and anthropometric data were collected from the participants. Public health officers experienced at intradermal immunisation, and nurses without experience, had 2 h of training on each of the administration methods before the campaign. Participants were vaccinated using the administration method in use by the vaccination team in their community. Poliovirus serum neutralising antibodies (SNA) were measured in children aged 24-59 months before and 4 weeks after vaccination. Adverse events and data on injection quality were collected from all participants. The primary outcome was the type 2 immune response rate (seroconversion in seronegative [SNA titre <8] children plus a 4-fold titre rise in seropositive children). Adjusted differences in the immune response between the DSJI or IDA group versus the N&S group were calculated with 97·5% CIs. A margin of -10% was used to define the non-inferiority of DSJI or IDA compared to N&S. Immunogenicity analysis was done per protocol. The trial is registered with ClinicalTrials.govNCT02967783 and has been completed.

FINDINGS

Between Oct 28 and Dec 29, 2016, 3189 children aged 4-59 months were recruited, of whom 3170 were eligible. Over 3 days, 2720 children were vaccinated (N&S, 917; IDA, 874; and DSJI, 929). Among 992 children aged 25-59 months with a baseline SNA available, 90·1% (95% CI 86·1-92·9; 281/312) of those vaccinated using the DSJI had an immune response to type 2 compared with 93·8% (90·6-95·8; 331/353) of those vaccinated with N&S and 96·6% (94·0-98·0; 316/327) of those vaccinated with IDA. All (53/53) type 2 seronegative children seroconverted. For polio type 2, non-inferiority was shown for both the IDA (adjusted difference 0·7% [97·5% CI -3·3 to 4·7], unadjusted difference 2·9% [-0·9 to 6·8]) and DSJI (adjusted difference -3·3% [-8·3 to 1·5], unadjusted difference -3·7% [-8·7 to 1·1]) compared with N&S. Non-inferiority was shown for type 1 and 3 for the IDA and DSJI. Neither injection quality nor the training and experience of the vaccinators had an effect on immune response. No safety concerns were reported.

INTERPRETATION

In a campaign, intradermal fIPV is safe and generates consistent immune responses that are not dependent on vaccinator experience or injection quality when administered using an N&S, DSJI, or IDA. Countries facing vaccine-derived poliovirus type 2 outbreaks should consider fIPV campaigns to boost population immunity and prevent cases of acute flaccid paralysis.

FUNDING

World Health Organization and the Medical Research Council.

Fractional dose compared with standard dose inactivated poliovirus vaccine in children: a systematic review and meta-analysis

BACKGROUND

Since WHO recommended introduction of at least a single dose of inactivated poliovirus vaccine (IPV) in routine immunisation schedules, there have been global IPV shortages. Fractional-dose IPV (fIPV) administration is one of the strategies to ensure IPV availability. We reviewed studies comparing the effects of fractional with full-dose IPV vaccination to determine when seroconversion proportions with each strategy become similar in children aged 5 years and younger.

METHOD

In this systematic review and meta-analysis, we searched 16 databases in July, 2019, for trials and observational studies, including ongoing studies that compare immunogenicity and adverse events of fractional-dose (0·1 mL) to full-dose (0·5 mL) IPV in healthy children aged 5 years or younger regardless of study design, number of doses, and route of administration. Screening, selection of articles, data extraction, and risk of bias assessment were done in duplicate, and conflicts were resolved by discussion or arbitration by a third author. We assessed immunogenicity, the main outcome, as proportion of seroconverted participants and changes in geometric mean titres of anti-poliovirus antibodies. Timepoints were eligible for analysis if measurements were done at least 4 weeks after vaccination. Summary estimates were pooled by use of random-effects meta-analysis. Analysis was stratified by study design, type of outcome measure, type of poliovirus, and number of doses given. We assessed heterogeneity using the χ² test of homogeneity and quantified it using the I² statistic. We assessed risk of bias using the Cochrane risk of bias tool, and the certainty of evidence using the Grading of Recommendations Assessment, Development and Evaluation approach. The study is registered with PROSPERO, CRD42018092647.

FINDINGS

860 records were screened for eligibility, of which 36 potentially eligible full-text articles were assessed and 14 articles were included in the final analysis: two ongoing trials and 12 articles reporting on ten completed studies. For poliovirus type 2, there were no significant differences in the proportions of seroconversions between fractional and full doses of IPV for two or three doses: the risk ratio for serconversion at one dose was 0·61 (95% CI 0·51-0·72), at two doses was 0·90 (0·82-1·00), and at three doses was 0·95 (0·91-1·00). Geometric mean titres (GMTs) for poliovirus type 2 were lower for fIPV than for full-dose IPV: -0·51 (95% CI -0·87 to -0·14) at one dose, -0·49 (-0·70 to -0·28) at two doses, and -0·98 (-1·46 to -0·51) at three doses. The seroconversion meta-analysis for the three-dose comparison was homogeneous (p=0·45; I²=0%), whereas heterogeneity was observed in the two-dose (p<0·00001; I²=88%) and one-dose (p=0·0004; I²=74%) comparisons. Heterogeneity was observed in meta-analyses of GMTs for one-dose (p<0·00001; I²=92%), two-dose (p=0·002; I²=80%), and three-dose (p<0·00001; I²=93%) comparisons. Findings for types 1 and 3 were similar to those for type 2. The certainty of the evidence was high for the three-dose comparisons and moderate for the rest of the comparisons.

INTERPRETATION

There is no substantial difference in seroconversion between three doses of fIPV and three doses of full-dose IPV, although the full dose gives higher titres of antibodies for poliovirus type 1, 2, and 3. Use of fractional IPV instead of the full dose can stretch supplies and possibly lower the cost of vaccination.

FUNDING

South African Medical Research Council and the National Research Foundation of South Africa.

Equivalent schedules of intradermal fractional dose versus intramuscular full dose of inactivated polio vaccine for prevention of poliomyelitis

BACKGROUND

Poliomyelitis is a debilitating and deadly infection. Despite exponential growth in medical science, there is still no cure for the disease, which is caused by three types of wild polioviruses: types 1, 2, and 3. According to the Global Polio Eradication Initiative (GPEI), wild poliovirus is still in circulation in three countries, and fresh cases have been reported even in the year 2018. Due to the administration of live vaccines, the risk for vaccine-derived poliovirus (VDPV) is high in areas that are free from wild polioviruses. This is evident based on the fact that VDPV caused 20 outbreaks between 2000 and 2011. Recent recommendations from the World Health Organization favoured the inclusion of inactivated poliovirus vaccine (IPV) in the global immunisation schedule. IPV can be delivered in two ways: intramuscularly and intradermally. IPV was previously administered intramuscularly, but shortages in vaccine supplies, coupled with the higher costs of the vaccines, led to the innovation of delivering a fractional dose (one-fifth) of IPV intradermally. However, there is uncertainty regarding the efficacy, immunogenicity, and safety of an intradermal, fractional dose of IPV compared to an intramuscular, full dose of IPV.

OBJECTIVES

To compare the immunogenicity and efficacy of an inactivated poliovirus vaccine (IPV) in equivalent immunisation schedules using fractional-dose IPV given via the intradermal route versus full-dose IPV given via the intramuscular route.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, 10 other databases, and two trial registers up to February 2019. We also searched the GPEI website and scanned the bibliographies of key studies and reviews in order to identify any additional published and unpublished trials in this area not captured by our electronic searches.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs of healthy individuals of any age who are eligible for immunisation with IPV, comparing intradermal fractional-dose (one-fifth) IPV to intramuscular full-dose IPV.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 13 RCTs involving a total of 7292 participants, both children (n = 6402) and adults (n = 890). Nine studies were conducted in middle-income countries, three studies in high-income countries, and only one study in a low-income country. Five studies did not report methods of randomisation, and one study failed to conceal the allocations. Eleven studies did not blind participants, and six studies did not blind outcome assessments. Two studies had high attrition rates, and one study selectively reported the results. Three studies were funded by pharmaceutical companies. Paralytic poliomyelitis. No study reported data on this outcome. Seroconversion rates. These were significantly higher for all three types of wild poliovirus for children given intramuscular full-dose IPV after a single primary dose and two primary doses, but only significantly higher for type two wild poliovirus given intramuscularly after three primary doses: • dose one (six studies): poliovirus type 1 (odds ratio (OR) 0.30, 95% confidence interval (CI) 0.22 to 0.41; 2570 children); poliovirus type 2 (OR 0.43, 95% CI 0.31 to 0.60; 2567 children); poliovirus type 3 (OR 0.19, 95% CI 0.12 to 0.30; 2571 children); • dose two (three studies): poliovirus type 1 (OR 0.23, 95% CI 0.16 to 0.33; 981 children); poliovirus type 2 (OR 0.41, 95% CI 0.28 to 0.60; 853 children); and poliovirus type 3 (OR 0.12, 95% CI 0.07 to 0.22; 855 children); and • dose three (three studies): poliovirus type 1 (OR 0.45, 95% CI 0.07 to 3.15; 973 children); poliovirus type 2 (OR 0.34, 95% CI 0.19 to 0.63; 973 children); and poliovirus type 3 (OR 0.18, 95% CI 0.01 to 2.58; 973 children). Using the GRADE approach, we rated the certainty of the evidence as low or very low for seroconversion rate (after a single, two, or three primary doses) for all three poliovirus types due to significant risk of bias, heterogeneity, and indirectness in applicability/generalisability. Geometric mean titres. No study reported mean antibody titres. Median antibody titres were higher for intramuscular full-dose IPV (7 studies with 4887 children); although these studies also reported a rise in antibody titres in the intradermal group, none reported the duration for which the titres remained high. Any vaccine-related adverse event. Five studies (2217 children) reported more adverse events, such as fever and redness, in the intradermal group, whilst two studies (1904 children) reported more adverse events in the intramuscular group.

AUTHORS' CONCLUSIONS

There is low- and very low-certainty evidence that intramuscular full-dose IPV may result in a slight increase in seroconversion rates for all three types of wild poliovirus, compared with intradermal fractional-dose IPV. We are uncertain whether intradermal fractional-dose (one-fifth) IPV has better protective effects and causes fewer adverse events in children than intramuscular full-dose IPV.