Oral Polio Vaccine Vaccination Research Articles

Can earlier BCG-Japan and OPV vaccination reduce early infant mortality? A cluster-randomised trial in Guinea-Bissau

ObjectiveTo assess the effect of providing BCG and oral polio vaccine (OPV) at an early home visit after delivery.DesignCluster-randomised trial, randomising 92 geographically defined clusters 1:1 to intervention/control arms.SettingBandim Health...

The second coming: The comeback of the live vaccines.

Live vaccines are gradually replaced by protein-based vaccines given the latter's better safety. But live vaccines seem to be more efficient via stimulation of the innate immune system.

Validation of a High-throughput, Multiplex, Real-time Qualitative Polymerase Chain Reaction Assay for the Detection of Sabin Oral Polio Vaccine in Environmental Samples.

BackgroundCurrently, the primary mechanism for poliovirus detection is acute flaccid paralysis (AFP) surveillance, with environmental sampling serving as a complement. However, as AFP cases drop, environmental surveillance will become increasingly critical for poliovirus detection. Mexico provides a natural environment to study oral polio vaccine (OPV) transmission, as it provides routine injected polio vaccine immunization and biannual OPV campaigns in February and May.MethodsAs part of a study of OPV transmission in which 155 children were vaccinated with OPV, monthly sewage samples were collected from rivers leading from 3 indigenous Mexican villages (Capoluca, Campo Grande, and Tuxpanguillo) from February to May 2015. Samples were also collected from October 2015 to October 2017, during which time there were standard OPV campaigns. Samples were analyzed for the presence of OPV serotypes, using a real-time qualitative polymerase chain reaction assay capable of detecting as few as 9, 12, and 10 copies/100 µL of viral ribonucleic acid for OPV serotypes 1, 2, and 3 (OPV-1, -2, and -3), respectively. Included here are 54 samples, taken up to November 2016.ResultsOf the 54 samples, 13 (24%) were positive for OPV. After the vaccination of 155 children in February 2015, OPV was found 2 months after vaccination. After unrestricted OPV administration in February 2016, OPV was detected in sewage up to 8 months after vaccination. OPV-3 was found in 11 of the 13 positive samples (85%), OPV-2 was found in 3 positive samples (23%), and OPV-1 was found in 1 sample (8%).ConclusionsOPV can be detected even when small amounts of the vaccine are introduced into a community, as shown by OPV-positive sewage samples even when only 155 children were vaccinated. When OPV vaccination was unrestricted, sewage samples were positive up to 8 months after vaccination, implying community OPV circulation for at least 8 months. OPV-3 was the serotype most found in these samples, indicating prolonged transmission of OPV-3 when compared to the other serotypes. Future work could compare the phylogenetic variance of OPV isolates from sewage after OPV vaccinations.

Assessing the stability of polio eradication after the withdrawal of oral polio vaccine.

The oral polio vaccine (OPV) contains live-attenuated polioviruses that induce immunity by causing low virulence infections in vaccine recipients and their close contacts. Widespread immunization with OPV has reduced the annual global burden of paralytic poliomyelitis by a factor of 10,000 or more and has driven wild poliovirus (WPV) to the brink of eradication. However, in instances that have so far been rare, OPV can paralyze vaccine recipients and generate vaccine-derived polio outbreaks. To complete polio eradication, OPV use should eventually cease, but doing so will leave a growing population fully susceptible to infection. If poliovirus is reintroduced after OPV cessation, under what conditions will OPV vaccination be required to interrupt transmission? Can conditions exist in which OPV and WPV reintroduction present similar risks of transmission? To answer these questions, we built a multi-scale mathematical model of infection and transmission calibrated to data from clinical trials and field epidemiology studies. At the within-host level, the model describes the effects of vaccination and waning immunity on shedding and oral susceptibility to infection. At the between-host level, the model emulates the interaction of shedding and oral susceptibility with sanitation and person-to-person contact patterns to determine the transmission rate in communities. Our results show that inactivated polio vaccine (IPV) is sufficient to prevent outbreaks in low transmission rate settings and that OPV can be reintroduced and withdrawn as needed in moderate transmission rate settings. However, in high transmission rate settings, the conditions that support vaccine-derived outbreaks have only been rare because population immunity has been high. Absent population immunity, the Sabin strains from OPV will be nearly as capable of causing outbreaks as WPV. If post-cessation outbreak responses are followed by new vaccine-derived outbreaks, strategies to restore population immunity will be required to ensure the stability of polio eradication.

National Immunization Campaigns with Oral Polio Vaccine Reduce All-Cause Mortality: A Natural Experiment within Seven Randomized Trials.

A recent WHO review concluded that live BCG and measles vaccine (MV) may have beneficial non-specific effects (NSEs) reducing mortality from non-targeted diseases. NSEs of oral polio vaccine (OPV) were not examined. If OPV vaccination campaigns reduce the mortality rate, it would suggest beneficial NSEs. Between 2002 and 2014, Guinea-Bissau had 15 general OPV campaigns and other campaigns with OPV plus vitamin A supplementation (VAS), VAS-only, MV, and H1N1 vaccine. In this period, we conducted seven randomized controlled trials (RCTs) with mortality as main outcome. Within these RCTs, we assessed whether the mortality rate was lower after-campaign than before-campaign. We used Cox models with age as underlying time and further adjusted for low birth-weight, season and time trend in mortality. We calculated the adjusted mortality rate ratio (MRR) for after-campaign vs before-campaign. The mortality rate was lower after OPV-only campaigns than before, the MRR being 0.81 (95% CI = 0.68-0.95). With each additional dose of campaign-OPV the mortality rate declined further (MRR = 0.87 (95% CI: 0.79-0.96) per dose) (test for trend, p = 0.005). No other type of campaign had similar beneficial effects. Depending on initial age and with follow-up to 3 years of age, the number needed to treat with campaign-OPV-only to save one life was between 68 and 230 children. Bissau had no case of polio infection so the results suggest that campaign-OPV has beneficial NSEs. Discontinuation of OPV-campaigns in low-income countries may affect general child mortality levels negatively.

Immunogenicity study to investigate the interchangeability among three different types of polio vaccine: A cohort study in Japan.

In Japan, the routine immunization program with oral polio vaccine (OPV) has been suspended since September 2012, when a program with 4 doses of inactivated monovalent polio vaccine (IPV) or quadrivalent vaccine against diphtheria, pertussis, and tetanus with IPV (DTaP-IPV) was introduced. The aim of this study was to examine the interchangeability among these 3 types of polio vaccines.We conducted a prospective cohort study at 5 pediatric clinics in Japan. A total of 153 infants were assigned to 1 of the 4 groups by considering the vaccination history of OPV and trivalent vaccine against DTaP. Eleven infants with a history of OPV received 3 doses of DTaP-IPV; 49 infants with a history of OPV and DTaP received 3 doses of IPV; 50 polio vaccine-naïve infants received 2 doses of IPV followed by 2 doses of DTaP-IPV; and 43 polio vaccine-naive infants received 2 doses of DTaP-IPV followed by IPV. The immunogenicity after polio vaccination was evaluated among these 4 groups.After 2 doses of polio vaccination, more than 80% of the infants exhibited a neutralization antibody titer ≥1:8 for all Sabin strains and wild strains in all groups. After the third dose, the seroprotection proportion (i.e., a neutralization antibody titer ≥1:8) reached about 100%. After the fourth dose, a neutralization antibody titer exceeded the required protective levels (i.e., a neutralization antibody titer ≥1:8) considerably in all groups.Four doses of polio vaccines induced a sufficient level of immunity in Japanese infants, irrespective of vaccine combinations or order.

Budget impact of polio immunization strategy for India: introduction of one dose of inactivated poliomyelitis vaccine and reductions in supplemental polio immunization

ObjectivesTo conduct a budget impact analysis (BIA) of introducing the immunization recommendations of India Expert Advisory Group (IEAG) for the years 2015–2017. The recommendations include introduction of one inactivated poliomyelitis vaccine (IPV) dose in the regular child immunization programme along with reductions in oral polio vaccine (OPV) doses in supplemental programmes. Study designThis is a national level analysis of budget impact of new polio immunization recommendations. Since the states of India vary widely in terms of size, vaccine coverage and supplemental vaccine needs, the study estimated the budget impact for each of the states of India separately to derive the national level budget impact. MethodsBased on the recommendations of IEAG, the BIA assumes that all children in India will get an IPV dose at 14 weeks of age in addition to the OPV and DPT (or Pentavalent-3) doses. Cost of introducing the IPV dose was estimated by considering vaccine price and vaccine delivery and administration costs. The cost savings associated with the reduction in number of doses of OPV in supplemental immunization were also estimated. The analysis used India-specific or international cost parameters to estimate the budget impact. ResultsIntroduction of one IPV dose will increase the cost of vaccines in the regular immunization programme from $20 million to $47 million. Since IEAG recommends lower intensity of supplemental OPV vaccination, polio vaccine cost of supplemental programme is expected to decline from $72 million to $53 million. Cost of administering polio vaccines will also decline from $124 million to $105 million mainly due to the significantly lower intensity of supplemental polio vaccination. The net effect of adopting IEAG's recommendations on polio immunization turns out to be cost saving for India, reducing total polio immunization cost by $6 million. Additional savings could be achieved if India adopts the new policy regarding the handling of multi-dose vials after opening. Introduction of three doses of IPV with the existing polio immunization schedule will increase the budget requirement by $102 million but replacing OPV doses with IPV will increase the budget by about $59 million. Discontinuation of supplemental OPV immunization with replacement of OPV by IPV will reduce the Government of India's (GOI) polio immunization budget by $99 million. ConclusionAlthough the overall cost of polio programme will decline with the adoption of IEAG's recommendations, state-level costs will vary widely. In states like Kerala, Karnataka, Uttar Pradesh and Andhra Pradesh, cost of polio immunization will increase while in Punjab and Jharkhand the costs will remain more or less constant. Significant cost reductions will happen in states with high intensity of supplemental polio immunizations (Bihar, Haryana and Delhi). The cost of procuring polio vaccines will more than double from $20 million to about $47 million requiring allocation of additional foreign exchanges. In some states (like Bihar), the decline in polio-related employment will be very high requiring reallocation of personnel from polio to other programmes.

Infant vaccination timing: Beyond traditional coverage metrics for maximizing impact of vaccine programs, an example from southern Nepal

BackgroundImmunization programs currently measure coverage by assessing the proportion of children 12–24 months who have been immunized but this does not address the important question of when the scheduled vaccines were administered. Data capturing the timing of vaccination in first 6 months, when severe disease is most likely to occur, are limited. ObjectiveTo estimate the time to Bacillus Calmette–Guérin (BCG) (recommended at birth), diphtheria-tetanus-pertussis-H, influenza b-hepatitis B (DTP-Hib-HepB), and oral polio vaccine (OPV) (recommended at 6, 10, and 14 weeks) vaccinations and risk factors for vaccination delay in infants <6 months of age in a district in southern Nepal where traditional coverage metrics are high. Design/methodsInfants enrolled in a randomized controlled trial of maternal influenza vaccination were visited weekly at home from birth through age 6 months to ascertain if any vaccinations had been given in the prior week. Infant, maternal, and household characteristics were recorded. BCG, DTP-Hib-HepB, and OPV vaccination coverage at 4 and 6 months was estimated. Time to vaccination was estimated through Kaplan–Meier curves; Cox-proportional hazards models were used to examine risk factors for delay for the first vaccine. ResultsThe median age of BCG, first OPV and DTP-Hib-HepB receipt was 22, 21, and 18 weeks, respectively. Almost half of infants received no BCG by age 6 months. Only 8% and 7% of infants had received three doses of OPV and DTP-Hib-HepB, respectively, by age 6 months. ConclusionA significant delay in receipt of infant vaccines was found in a prospective, population-based, cohort in southern Nepal despite traditional coverage metrics being high. Immunization programs should consider measuring time to receipt relative to the official schedule in order to maximize benefits for disease control and child health.

Characteristics of persons refusing oral polio vaccine during the immunization plus days - Sokoto, Nigeria 2011.

IntroductionNigeria, the only African country endemic for wild poliovirus, adopted Immunization Plus Days (IPD) to eradicate polio. Refusal of oral polio vaccine (OPV) by heads of households is a significant challenge. In Sokoto state, we determined characteristics of heads of households refusing OPV during IPD in 2011.MethodsTo evaluate reasons for refusals, we conducted a case control study among heads ofhouseholds accepting or refusing OPV vaccine. Noncompliant households were defined as households refusing OPV vaccination in last three rounds of IPDs while compliant households were those accepting vaccination. Interviewers administered a questionnaire to the heads of households to obtain information on socio-demographics, media habits, and knowledge of IPD.ResultsOf the 121 (60 cases and 61 controls) interviews, 88 (73%) were from Sokoto north. Noncompliant heads of households were more likely to lack tertiary education (OR = 3.7, 95% CI, 1.6 - 9.2), believe that OPV is not safe (OR = 22, 95% CI, 7.1 - 76), lack access to functional radio (OR = 4.4, 95% CI, 1.4 - 15) and television (OR = 9.4, 95% CI, (1.9 - 63) andget information about IPD from town announcers (OR = 3.9, 95% CI, 1.3 - 12).ConclusionWe conclude that noncompliant heads of households compared to compliant heads of households had low level of education, lacked knowledge of immunization, and had negative attitude towards OPV. They get information about OPV from town announcers and lacked access to functional radio and television. We recommended training of town announcers in polio communication and use of key communication messages preceding every round of IPD.

Characteristics of persons refusing oral polio vaccine during the immunization plus days – Sokoto, Nigeria 2011

INTRODUCTION: Nigeria, the only African country endemic for wild poliovirus, adopted Immunization Plus Days (IPD) to eradicate polio. Refusal of oral polio vaccine (OPV) by heads of households is a significant challenge. In Sokoto state, we determined characteristics of heads of households refusing OPV during IPD in 2011. METHODS: To evaluate reasons for refusals, we conducted a case control study among heads ofhouseholds accepting or refusing OPV vaccine. Noncompliant households were defined as households refusing OPV vaccination in last three rounds of IPDs while compliant households were those accepting vaccination. Interviewers administered a questionnaire to the heads of households to obtain information on socio-demographics, media habits, and knowledge of IPD. RESULTS: Of the 121 (60 cases and 61 controls) interviews, 88 (73 %) were from Sokoto north. Noncompliant heads of households were more likely to lack tertiary education (OR=3.7, 95 % CI, 1.6 - 9.2), believe that OPV is not safe (OR=22, 95 % CI, 7.1 - 76), lack access to functional radio (OR=4.4, 95 % CI, 1.4 - 15) and television (OR=9.4, 95 % CI, (1.9 - 63) andget information about IPD from town announcers (OR=3.9, 95 % CI, 1.3 - 12). CONCLUSION: We conclude that noncompliant heads of households compared to compliant heads of households had low level of education, lacked knowledge of immunization, and had negative attitude towards OPV. They get information about OPV from town announcers and lacked access to functional radio and television. We recommended training of town announcers in polio communication and use of key communication messages preceding every round of IPD.

Reemergence of Recombinant Vaccine–derived Polioviruses in Healthy Children, Madagascar

Reemergence of Recombinant Vaccine–derived Polioviruses in Healthy Children, Madagascar

A study evaluating poliovirus antibodies and risk factors associated with polio seropositivity in low socioeconomic areas of Pakistan

BackgroundSeroprevalence studies provide important data on performance of immunization programs, susceptible groups and populations at-risk of future outbreaks. Identifying risk factors that affect seroconversion of the oral polio vaccine (OPV) will enable the polio eradication initiatives to increase seroprevalence. This paper describes the first population-based seroprevalence survey in Pakistan. MethodsThis study evaluated the seroprevalence of poliovirus (PV) types 1, 2, and 3 antibodies to OPV in an illustrative sample of 554 subjects 6–11 months of age in three geographic locations of Pakistan (Lahore, Karachi, and Peshawar) representing a low socioeconomic at-risk populations. Antibody titers were measured and sero protection rates and geometric median titers were compared among different geographic regions and populations, as were demographics and OPV vaccination history collected by questionnaire. Univariate and multivariate analyses were conducted on subject characteristics to assess for potential risk factors for failure to sero-convert. ResultsThe average seroprevalence of PV1, PV2, and PV3 was 96.0%, 87.9% and 86.7%, respectively. The lowest sero protection rate for all three serotypes was for Karachi with 90.2%, 73.8%, and 78.8% for PV1, PV2, and PV3, respectively. Significant regional variation in PV3 seroprevalence was found (range: 74.2–100%). In the univariate analysis, age, total and campaign OPV doses were associated with higher seroprevalence, whereas stunting, respondent education and diarrhea in the past six months were significant risk factors for failure to sero-convert. ConclusionsThese findings demonstrate consistently high levels of antibody response to PV1 and more geographically varied response to PV2 and PV3. Additionally, important risk factors affecting seropositivity were identified.

Inactivated Polio Vaccine: its proposed role in the final stages of polio eradication

In 2000, the island of Hispaniola, home to Haiti and the Dominican Republic, was the first place where the existence of circulating vaccine derived poliovirus (cVDPV) was demonstrated. As a live product, oral polio vaccine (OPV), once excreted, could enter the environment, reassort with other enteroviruses, and produce cVDPV. After the investigation of that outbreak, the first of a dozen in the current century, a review of laboratory samples from elsewhere showed that other cVDPV had circulated in countries, notably Egypt, and was misclassified as wild poliovirus (WPV) at the time. It was recognized that the extent of cVDPV was large enough to pose a threat to the global eradication programme. In the current century, cVDPV has been found in countries as diverse as China and Madagascar, with three recent cases seen in Kenya, genetically linked to Somalia. A 2008 review of the first eight documented outbreaks, all from countries with poor OPV vaccination coverage, was not reassuring.

PER.C6® cells as a serum-free suspension cell platform for the production of high titer poliovirus: A potential low cost of goods option for world supply of inactivated poliovirus vaccine

There are two highly efficacious poliovirus vaccines: Sabin's live-attenuated oral polio vaccine (OPV) and Salk's inactivated polio vaccine (IPV). OPV can be made at low costs per dose and is easily administrated. However, the major drawback is the frequent reversion of the OPV vaccine strains to virulent poliovirus strains which can result in Vaccine Associated Paralytic Poliomyelitis (VAPP) in vaccinees. Furthermore, some OPV revertants with high transmissibility can circulate in the population as circulating Vaccine Derived Polioviruses (cVDPVs). IPV does not convey VAPP and cVDPVs but the high costs per dose and insufficient supply have rendered IPV an unfavorable option for low and middle-income countries.Here, we explored whether the human PER.C6® cell-line, which has the unique capability to grow at high density in suspension, under serum-free conditions, could be used as a platform for high yield production of poliovirus. PER.C6® cells supported replication of all three poliovirus serotypes with virus titers ranging from 9.4log10 to 11.1log10TCID50/ml irrespective of the volume scale (10ml in shaker flasks to 2L in bioreactors). This production yield was 10–30 fold higher than in Vero cell cultures performed here, and even 100-fold higher than what has been reported for Vero cell cultures in literature [38]. In agreement, the D-antigen content per volume PER.C6®-derived poliovirus was on average 30-fold higher than Vero-derived poliovirus. Interestingly, PER.C6® cells produced on average 2.5-fold more D-antigen units per cell than Vero cells.Based on our findings, we are exploring PER.C6® as an interesting platform for large-scale production of poliovirus at low costs, potentially providing the basis for global supply of an affordable IPV.

History of polio vaccination

Poliomyelitis is an acute paralytic disease caused by three poliovirus (PV) serotypes. Less than 1% of PV infections result in acute flaccid paralysis. The disease was controlled using the formalin-inactivated Salk polio vaccine (IPV) and the Sabin oral polio vaccine (OPV). Global poliomyelitis eradication was proposed in 1988 by the World Health Organization to its member states. The strategic plan established the activities required for polio eradication, certification for regions, OPV cessation phase and post-OPV phase. OPV is the vaccine of choice for the poliomyelitis eradication program because it induces both a systemic and mucosal immune response. The major risks of OPV vaccination are the appearance of Vaccine-Associated Paralytic Poliomyelitis cases (VAPP) and the emergence of Vaccine Derived Polioviruses strains. The supplementary immunization with monovalent strains of OPV type 1 or type 3 or with a new bivalent oral polio vaccine bOPV (containing type 1 and type 3 PV) has been introduced in those regions where the virus has been difficult to control. Most countries have switched the schedule of vaccination by using IPV instead of OPV because it poses no risk of vaccine-related disease. Until 2008, poliomyelitis was controlled in Romania, an Eastern European country, predominantly using OPV. The alternative vaccination schedule (IPV/OPV) was implemented starting in September 2008, while beginning in 2009, the vaccination was IPV only. The risk of VAPP will disappear worldwide with the cessation of use of OPV. The immunization for polio must be maintained for at least 5 to 10 years using IPV.

Immunity status of adults and children against poliomyelitis virus type 1 strains CHAT and Sabin (LSc-2ab) in Germany.

BackgroundIn October 2007, the working group CEN/TC 216 of the European Committee for standardisation suggested that the Sabin oral poliovirus vaccine type 1 strain (LSc-2ab) presently used for virucidal tests should be replaced by another attenuated vaccine poliovirus type 1 strain, CHAT. Both strains were historically used as oral vaccines, but the Sabin type 1 strain was acknowledged to be more attenuated. In Germany, vaccination against poliomyelitis was introduced in 1962 using the oral polio vaccine (OPV) containing Sabin strain LSc-2ab. The vaccination schedule was changed from OPV to an inactivated polio vaccine (IPV) containing wild polio virus type 1 strain Mahoney in 1998. In the present study, we assessed potential differences in neutralising antibody titres to Sabin and CHAT in persons with a history of either OPV, IPV, or OPV with IPV booster.MethodsNeutralisation poliovirus antibodies against CHAT and Sabin 1 were measured in sera of 41 adults vaccinated with OPV. Additionally, sera from 28 children less than 10 years of age and immunised with IPV only were analysed. The neutralisation assay against poliovirus was performed according to WHO guidelines.ResultsThe neutralisation activity against CHAT in adults with OPV vaccination history was significantly lower than against Sabin poliovirus type 1 strains (Wilcoxon signed-rank test P < 0.025). In eight sera, the antibody titres measured against CHAT were less than 8, although the titre against Sabin 1 varied between 8 and 64. Following IPV booster, anti-CHAT antibodies increased rapidly in sera of CHAT-negative adults with OPV history. Sera from children with IPV history neutralised CHAT and Sabin 1 strains equally.ConclusionThe lack of neutralising antibodies against the CHAT strain in persons vaccinated with OPV might be associated with an increased risk of reinfection with the CHAT polio virus type 1, and this implies a putative risk of transmission of the virus to polio-free communities. We strongly suggest that laboratory workers who were immunised with OPV receive a booster vaccination with IPV before handling CHAT in the laboratory.

Population dynamics of live-attenuated virus vaccines

Viruses contained in live-attenuated virus vaccines (LAVV) can be transmitted between individuals, resulting in secondary or contact vaccinations. This fact has been exploited successfully in the use of the Oral Polio Vaccine (OPV) to better control wild-type polio viruses. In this work we analyze general LAVV vaccination models for infections that confer lifelong immunity. We consider both standard (continuous) vaccination strategies and pulse vaccination programs (where mass vaccination is carried out at regular intervals). For continuous vaccination, we provide a complete global analysis of a very general compartmental ordinary differential equation LAVV model. We find that the threshold vaccination level required for the eradication of wild-type virus depends on the basic reproduction numbers of both the wild-type and vaccine viruses, but is otherwise independent of the distributions of the durations in each of the sequence of stages of disease progression (e.g., latent, infectious, etc.). Furthermore, even for vaccine viruses with reproduction numbers below one, which would naturally fade from the population upon cessation of vaccination, there can be a significant reduction in the threshold vaccination level. The dependence of the threshold vaccination level on the virus reproduction numbers largely generalizes to the pulse vaccination model. For shorter pulsing periods there is negligible difference in threshold vaccination level as compared to continuous vaccination campaigns. Thus, we conclude that current policy in many countries to employ annual pulsed OPV vaccination does not significantly diminish the benefits of contact vaccination.

Circulating Vaccine Derived Polio Viruses and their Impact on Global Polio Eradication

Poliomyelitis vaccination via live Oral Polio Vaccine (OPV) suffers from the inherent problem of reversion: the vaccine may, upon replication in the human gut, mutate back to virulence and transmissibility resulting in circulating vaccine derived polio viruses (cVDPVs). We formulate a general mathematical model to assess the impact of cVDPVs on prospects for polio eradication. We find that for OPV coverage levels below a certain threshold, cVDPVs have a small impact in comparison to the expected endemic level of the disease in the absence of reversion. Above this threshold, the model predicts a small but significant endemic level of the disease, even where standard models predict eradication. In light of this, we consider and analyze three alternative eradication strategies involving a transition from continuous OPV vaccination to either continuous Inactivated Polio Vaccine (IPV), pulsed OPV vaccination, or a one-time IPV pulse vaccination. Stochastic modeling shows continuous IPV vaccination is effective at achieving eradication for moderate coverage levels, while pulsed OPV is effective if higher coverage levels are maintained. The one-time pulse IPV method may also be a viable strategy, especially in terms of the number of vaccinations required and time to eradication, provided that a sufficiently large pulse is practically feasible. More investigation is needed regarding the frequency of revertant virus infection resulting directly from vaccination, the ability of IPV to induce gut immunity, and the potential role of spatial transmission dynamics in eradication efforts.

Knowledge and practice of oral polio vaccine-vaccine vial monitor among health personnel in India

Knowledge and practice of oral polio vaccine-vaccine vial monitor among health personnel in India

Vaccine-derived polioviruses

The Sabin oral poliovaccine (OPV) is extremely efficacious and safe, despite its inherent genetic instability. While reversion to nearly wild-type phenotype regularly occurs soon after the onset of OPV reproduction in the gastro-intestinal tract of vaccine recipients or their contacts, this is usually not a big problem, provided the vaccine is used either for mass vaccination or in populations with a relatively high level of anti-polio immunity. However, if these conditions are not met, the vaccine viruses are likely to be converted into highly transmissible agents with a nearly wild-type level of neurovirulence. Moreover, OPV viruses may persist and evolve even in adequately immunized populations. The current strategy for the “endgame” of poliovirus eradication envisions cessation of OPV usage shortly after the last isolation of a wild poliovirus. If implemented, this strategy would result in rapid growth of non-immune human populations at the time when OPV derivatives would very likely be persisting. Therefore, the planned cessation of OPV vaccination is associated with a very high, and in the author's opinion, unacceptable risk of polio outbreaks caused by OPV derivatives. The only currently available tool to curb such outbreaks is OPV, which should have been used at a global scale. Safe discontinuation of OPV vaccination will be possible only after an efficient new vaccine or an anti-poliovirus drug is available. To achieve this goal, stimulation of poliovirus research and elimination of organizational and financial obstacles preventing it are needed.