Festus Adu

Multiple Independent Emergences of Type 2 Vaccine-Derived Polioviruses during a Large Outbreak in Northern Nigeria

ABSTRACT Since 2005, a large poliomyelitis outbreak associated with type 2 circulating vaccine-derived poliovirus (cVDPV2) has occurred in northern Nigeria, where immunization coverage with trivalent oral poliovirus vaccine (tOPV) has been low. Phylogenetic analysis of P1/capsid region sequences of isolates from each of the 403 cases reported in 2005 to 2011 resolved the outbreak into 23 independent type 2 vaccine-derived poliovirus (VDPV2) emergences, at least 7 of which established circulating lineage groups. Virus from one emergence (lineage group 2005-8; 361 isolates) was estimated to have circulated for over 6 years. The population of the major cVDPV2 lineage group expanded rapidly in early 2009, fell sharply after two tOPV rounds in mid-2009, and gradually expanded again through 2011. The two major determinants of attenuation of the Sabin 2 oral poliovirus vaccine strain (A481 in the 5′-untranslated region [5′-UTR] and VP1-Ile143) had been replaced in all VDPV2 isolates; most A481 5′-UTR replacements occurred by recombination with other enteroviruses. cVDPV2 isolates representing different lineage groups had biological properties indistinguishable from those of wild polioviruses, including efficient growth in neuron-derived HEK293 cells, the capacity to cause paralytic disease in both humans and PVR-Tg21 transgenic mice, loss of the temperature-sensitive phenotype, and the capacity for sustained person-to-person transmission. We estimate from the poliomyelitis case count and the paralytic case-to-infection ratio for type 2 wild poliovirus infections that ∼700,000 cVDPV2 infections have occurred during the outbreak. The detection of multiple concurrent cVDPV2 outbreaks in northern Nigeria highlights the risks of cVDPV emergence accompanying tOPV use at low rates of coverage in developing countries.

Outbreak of Type 2 Vaccine-Derived Poliovirus in Nigeria: Emergence and Widespread Circulation in an Underimmunized Population

Wild poliovirus has remained endemic in northern Nigeria because of low coverage achieved in the routine immunization program and in supplementary immunization activities (SIAs). An outbreak of infection involving 315 cases of type 2 circulating vaccine-derived poliovirus (cVDPV2; >1% divergent from Sabin 2) occurred during July 2005–June 2010, a period when 23 of 34 SIAs used monovalent or bivalent oral poliovirus vaccine (OPV) lacking Sabin 2. In addition, 21 “pre-VDPV2” (0.5%–1.0% divergent) cases occurred during this period. Both cVDPV and pre-VDPV cases were clinically indistinguishable from cases due to wild poliovirus. The monthly incidence of cases increased sharply in early 2009, as more children aged without trivalent OPV SIAs. Cumulative state incidence of pre-VDPV2/cVDPV2 was correlated with low childhood immunization against poliovirus type 2 assessed by various means. Strengthened routine immunization programs in countries with suboptimal coverage and balanced use of OPV formulations in SIAs are necessary to minimize risks of VDPV emergence and circulation.

Resistance of recent measles virus wild-type isolates to antibody-mediated neutralization by vaccinees with antibody

The neutralization capacity of sera from Luxembourgian adolescent vaccinees and from Nigerian women with measles‐induced immunity to a number of measles virus strains was compared. Although both cohorts were matched for their hemagglutination inhibition and standard neutralization titers, 12 of the 22 late convalescent sera, and only 6 of 24 vaccinees neutralized all viruses. Similarly, only 2 of 20 viruses were not neutralized by at least 75% of late convalescent sera, in comparison to 10 of 20 viruses that resisted neutralization by at least 75% of the vaccinees. The more resistant viruses were not limited to a certain clade. One Nigerian virus was resistant to neutralization by 30% of the late convalescent women and by 75% of vaccinees. These results suggest that qualitative differences in neutralizing antibodies may reduce further protection of infants by passively acquired immunity against wild‐type viruses when vaccinated girls become mothers. J. Med. Virol. 62:91–98, 2000.

Molecular characterization of diverse species enterovirus-B types from children with acute flaccid paralysis and asymptomatic children in Nigeria.

Non-polio enteroviruses (NPEVs) have often been identified in association with acute flaccid paralysis (AFP) in most polio surveillance studies worldwide. In a polio endemic country like Nigeria, there is need for distinction of AFP due to poliovirus and those potentially due to NPEVs. This study was undertaken to characterize the enterovirus (EV) types circulating in both children with and without AFP in Nigeria. Of fecal sample from 966 children with AFP, 96 (10%) were positive for NPEVs in RD cells, while 42 (5.5%) of 756 samples from non-AFP children was positive. Genotyping of all NPEV isolates was done by partial VP1 gene sequencing and phylogenetic analysis. EV-B was the predominant species detected (84%) and infection was common in children with AFP with CVB3, E6, and E11 constituting the predominant types detected. The CVB3 isolates cluster with Chinese CVB3 isolate recently detected in a newborn with AFP. There was also a remarkable clustering of isolates such as E6, E12, E13, E24, E30 and E33 to types previous detected in West Africa suggesting a probable circulation of these lineages in the region. Taken together, this study reveals a diverse species EV-B types in AFP cases and highlights the fact that other neurotropic EVs circulate in asymptomatic persons. Improved continuous surveillance of NPEV is warranted as in the likely attainment of polio eradication, other neurotropic EVs may emerge causing similar paralytic diseases.

Phylogenetics and Pathogenesis of Early Avian Influenza Viruses (H5N1), Nigeria

Three highly pathogenic avian influenza subtype H5N1 and 4 Newcastle disease viruses were isolated from sick or dead chickens in southwestern Nigeria. Sequencing and phylogenetic analysis placed them within H5N1 subclade 2.2.2. Intravenous and intranasal pathogenicity tests produced systemic disease with vascular endothelial cell tropism in chickens.

Some genetic characteristics of sabin-like poliovirus isolated from acute flaccid paralysis cases in Nigeria

A total of 34 sabin strains of the poliovirus isolated from 22 children with 60-day follow-up residual acute flaccid paralysis (AFP) were genetically characterized and screened for any form of recombination. Sequence analysis of the 906-nucleotide capsid showed that all the isolates were similar to their original sabin serotypes, however two of the viruses had drifted in their 3D noncapsid regions toward a sabin-sabin and sabin-nonpolio entero combination. Routine immunization in Nigeria is low and in spite of the increase in the frequency of supplemental immunizations, a lot of children are still inadequately immunized, which may be the reason for our observation in this study. Although we are not dealing with a case of circulating vaccine derived poliovirus (cVDPV) yet, if the above condition persists, the advent of cVDVP may not be too far. There is therefore the need to maintain a high quality mass immunization and sustained routine immunization. Key words : Poliovirus, sequence, crossover, non polio enterovirus, recombination, genome, Sabin-like, vaccine, Nigeria. African Journal of Biotechnology Vol.2(11) 2003: 460-464

Measles Vaccine Potency and Sero-Conversion Rates among Infants Receiving Measles Immunization in Ilorin, Kwara State, Nigeria

This study was designed to assess the seroconversion rate of measles vaccine among infants receiving measles immunization in Ilorin, Nigeria. The pre- and post-measles vaccination sera of the children were tested using the Haemagglutination Inhibition test. The measles vaccines administered at the immunization centre were also tested for their potency using in-vitro titration method. Only 286 (71.5%) of the vacinees returned to give post-vaccination samples. All the infants screened had low pre-vaccination measles antibody titers. Thirty one (8.0%) of the infants had measles prior to vaccination. The seroconversion pattern showed that 196 (68.6%) of the infants developed protective antibody titers. Low seroconversion rate reported in this study was due to low vaccine potency. The titers of vaccines with low potency ranged between log10−1.0–log10−2.25 TCID/per dose. This was beside other non specific antiviral substances exhibited virus neutralizing activity. Only 3 (50%) of the 6 vaccine vials tested had virus titers of log10−3.25 to log10−3.5, which fell above the cut-off point recommended by the World Health Organization for measles vaccines. The sero-conversion rate of 68.6% observed among vaccinees is far lower than the immunity level of 95% required stopping measles transmission in an endemic community. Failure of 31.4% of these infants to sero-convert post vaccination can be attributed partly to administration of sub-potent vaccines. There is need for improvement and maintenance of effective vaccine cold chain system in Nigeria. There is need also for periodic monitoring of post-vaccination antibody titers as well as vaccine potency status in order to ensure development of protective seroconversion rates.

Persistence of poliomyelitis in Nigeria

The World Health Assembly launched the Global Polio Eradication Initiative in 1988 and declared the year 2000 as the target by which to achieve poliomyelitis eradication. After aggressive mass immunisation, backed up by eff ective routine immunisation, cases of poliomyelitis reduced from 350 000 in 165 countries in 1988 to 355 occurring mainly in three countries— Nigeria, Afghanistan, and Pakistan—by 2013. Nigeria is the only country in the world where the three poliovirus types are still circulating; as of December, 2013, it had contributed 14·1% of all poliomyelitis cases worldwide. In the past 4 years, Nigerian Government and donor investments have increased and traditional leaders have committed to poliomyelitis eradication. Despite all these eff orts and many years of mass vaccination campaigns, wild poliovirus continues to circulate in the northern part of the country, leading stakeholders to wonder whether something hidden or unknown is aff ecting the vaccination programme in Nigeria. In The Lancet Global Health, Tara Mangal and colleagues report the results of their case-control study into the persistence of poliomyelitis in Nigeria, which identifi ed low vaccine effi cacy, poor vaccine coverage, suboptimum population immunity, rejection and refusal of vaccine, and lack of awareness as issues responsible for the persistence of the virus in Nigeria. A report by the Nigerian Expert Review Committee on Polio Eradication following their 25th meeting in September, 2012, also identifi ed a lack of shared sense of emergency by some states, slow improvement in poliomyelitis campaign performance in some local government areas, and neglect of routine immunisation as reasons compromising the success of the programme. Although these fi ndings represent substantial quantifi able and perceivable reasons, and have added to the understanding about poliomyelitis in Nigeria, in our opinion there are other obscure and intractable factors contributing to the problems facing poliomyelitis eradication in Nigeria. The issues aff ecting poliomyelitis eradication can be linked to larger problems aff ecting the whole country. Political, cultural, and religious considerations often dictate attitudes and the course of action in Nigeria. Notably, the 2004 rejection of the oral poliovirus vaccine in the northern part of the country followed the election result, which some leaders from the northern part of the country felt was not in their favour. Nigeria was close to eradicating poliomyelitis in 2004 when the campaign against the oral poliovirus vaccine began. That action is still aff ecting the programme now, although its eff ect has been signifi cantly reduced by the involvement of political, community, and religious leaders, and intensifi ed communication strategies. Diff erences in culture and social behaviour have contributed substantially to the persistence of poliomyelitis in the country. In some parts of the country, a paralysed child is seen as a taboo; as such, people living in these areas are greatly aware of the importance of vaccination. Minimal eff ort is needed to convince caregivers to take those under their protection to be vaccinated in these regions. This awareness is not apparent in other parts of the country, where most paralysed children have to turn to begging in the streets. In such a situation, a single defi ant infl uential voice, asking people to reject and refuse the vaccine, is suffi cient to turn the programme from success to failure. The level of education of caregivers, especially mothers, is crucial. Education leads to better understanding, knowledge, and attitudes. A well informed, educated mother is capable of making an independent benefi cial decision on her own, and can be easily convinced about the advantages and disadvantages of acceptance or refusal of vaccines. Neither of the two major religions (Islam and Christianity) is against immunisation, but a lack of awareness, low social status, and high illiteracy levels can easily turn a willing mother into a defi ant, non-compliant caregiver. All these factors are directly responsible for many children not being vaccinated, which has been the major reason for the persistent circulation of the virus in Nigeria. For the total success of the programme, these factors have to be addressed. Fortunately, new strategic approaches to address some of these factors have been put in place. New stepbased approaches for change—addressing the issues of demand, refusal, and rejection, and reaching out to chronically unvaccinated children—as well as an increase in routine immunisation coverage, increased and intensifi ed communication strategies addressing noncompliance, and improved supplementary immunisation activities, have produced good results. Impressive achievements have been made in the last 9 months. See Articles page e90

DETERMINATION OF MEASLES HEMAGGLUTINATION INHIBITING ANTIBODY LEVELS AMONG SCHOOL CHILDREN IN IBADAN, NIGERIA

Immune status of school children aged from 10–23 years against measles virus was determined by the hemagglutination-inhibition (HI) test with a view of assessing herd immunity. Blood samples from 500 schoolchildren were collected by finger-pricking in Ropacco filter papers. Sera were extracted in 1 mL of cold phosphate buffered saline and treated with 25% (w/v) kaolin and 50.0% monkey red blood cell (RBC) to a final concentration of 1:10. The measles hemagglutinating antigen used for the test was prepared from measles vaccine. Results showed that 62 (12.4%) were positive for measles HI antibody at a titer of 1:640, and 78 (15.6%) had a titer <1:10. There was no significant relationship (P > 0.05) between antibody titer and the schools, while a significant relationship (P < 0.05) existed between antibody titer and age. Although the majority of the schoolchildren had the measles antibody in their sera, titers were, however, beneath the threshold of protection in 33.4% of them. The significant association between age of the schoolchildren and HI titers showed that those antibodies were waning according to age. The study has shown a considerable high level of protection against measles among schoolchildren. To prevent future outbreak of measles among these schoolchildren, it will be advocated that a second dose of measles vaccine be administered.

Comparative Study of Molecular and Antigenic Characterization for Intratypic Differentiation (ITD) of Poliovirus Strains

This study was designed to compare the sensitivity of a Sabin vaccine strain‐specific PCR assay and an enzyme‐linked immunosorbent assay with polyclonal cross‐absorbed antisera (PAb‐E) for intratypic differentiation (ITD) of polioviruses (PVs). These were used for the definitive characterization of the strains. Poliovirus strains isolated in L20B and RD cell lines were subjected to both PCR and ELISA. Both PCR and ELISA identified 3 (13.6%) out of 22 isolates, respectively as poliovirus Sabin 1. PCR identified 4 (18.2%) out of 22 isolates as poliovirus Sabin 2 and ELISA identified 2 (9.1%) out of 22 isolates as poliovirus Sabin 2. None of the two assay identified poliovirus Sabin 3. Both PCR and ELISA identified 12 (54.5%) out of 22 isolates, respectively as wild poliovirus (WPV) 1. None of the assays identified any of the isolates as WPV 2 and 3. Only PCR assay was able to identify the mixture of two poliovirus Sabin serotypes (a mixture of Sabin 1 and 2) and two mixtures of poliovirus Sabin 2 and 3. In this study, only ELISA was able to identified two invalid results. Invalid results observed in this study are of important practical implication to the emergence of vaccine‐derived poliovirus. This may have epidemic potential. Hence, the two ITD assays are of paramount importance for identification of PVs. It is therefore recommended in line with WHO guideline that at least two methods be used for the ITD of poliovirus isolates, and each method should be based on a different principle (i.e., antigenic and genetic properties). J. Med. Virol. 84:1975–1979, 2012.