Temporal and Spatial Dynamics of Vaccine-Derived Poliovirus (VDPV) in Democratic Republic of Congo from 2018 to 2023

Background: The Democratic Republic of Congo (DRC) has been facing outbreaks of VDPV since 2017. These wild poliovirus variants are responsible for poliomyelitis, which is in the process of eradication.. In the following lines, we try to show the evolution of VDPV cases across the country in order to understand their chronological dynamics and seasonal influence. Methods: We conducted a cross-sectional study of of VDPV notified in the DRC from 2018 to 2023. Maps of the spatial dynamics of VDPV cases were produced from attack rates with QGIS® (3.22.8). As for temporal dynamics, time series were decomposed and presented in the form of graphs showing the chronological evolution of VDPV cases and their seasonal trend, using R.4.0 software package. Results: A total of 1196 Cases of VDPV types 1, 2 and 3 were recorded in the biological confirmation databases of the INRB and the Expanded Program of Immunization during the study period across25 provinces. The eastern part of the country reporting the most cases. The general trend is upwards, with a peak in 2022 of 527 cases, whereas in 2021 there was a notable drop of 31 cases. Analysis of the temporal breakdown suggests a seasonal pattern, with peaks between the months of September and December, considered being rainy periods in some provinces. Conclusion: During the 6 years of our study (2018 - 2023) almost all the Health Zones were hit by VDPV epidemics. The eastern part was the most impacted. The seasonal component is well marked suggesting a rise in detection in the rainy season and during pivotal periods of climate change.

Stochastic Analysis for the Dynamics of a Poliovirus Epidemic Model

Most developing countries such as Afghanistan,Pakistan,India,Bangladesh,and many more are still fighting against poliovirus.According to the World Health Organization,approximately eighteen million people have been infected with poliovirus in the last two decades.In Asia,still,some countries are suffering from the virus.The stochastic behavior of the poliovirus through the transition probabilities and non-parametric perturbation with fundamental properties are studied.Some basic properties of the deterministic model are studied,equilibria,local stability around the stead states,and reproduction number.Euler Maruyama,stochastic Euler,and stochastic Runge-Kutta study the behavior of complex stochastic differential equations.The main target of this study is to develop a nonstandard computational method that restores dynamical features like positivity,boundedness,and dynamical consistency.Unfortunately,the existing methods failed to fix the actual behavior of the disease.The comparison of the proposed approach with existing methods is investigated.

Regulations for the Manufacture and Control of Live Poliovirus Vaccine: International Experience and China’s Path

The eradication of poliomyelitis is a landmark achievement in the history of public health, providing strong protection for children’s health. The introduction of the Chinese Regulations for the Manufacture and Control of Live Poliovirus Vaccine is a prerequisite and safeguard for the large-scale production and use of domestically produced live poliovirus vaccines, serving as an indispensable component of vaccine safety. This article, based on archival documents, letters, collections of essays, and oral interviews, examines the historical experience of the development of Chinese Regulations for the Manufacture and Control of Live Poliovirus Vaccine. It contends that the emphasis on localization and the active engagement in international cooperation are critical factors in the swift introduction of Chinese Regulations for the Manufacture and Control of Live Poliovirus Vaccine.

Pediatric case with vaccine-related poliovirus infection: A case report

BACKGROUND As long as oral poliovirus vaccine(OPV)is used,the potential risk for the emergence of vaccine-related polioviruses remains.CASE SUMMARY We report a case of Sabin-like type 1 poliovirus infection in an immunocompetent 17-mo-old child after receiving four scheduled doses of OPV.Somehow,the four doses did not confer full protection,possibly because of interference created by other enteroviruses.CONCLUSION The surveillance of vaccine-related polioviruses has important implications for improving health policies and vaccination strategies.Missed cases of vaccinerelated poliovirus infection might pose a potential risk to global poliovirus eradication.Therefore,the global withdrawal of OPV and a shift to the inclusion of only inactivated poliovirus vaccine in the vaccination schedule is the main objective of the polio eradication program.

Inactivation of Poliovirus by Ozone and the Impact of Ozone on the Viral Genome

Objective To investigate the mechanisms underlying ozone-induced inactivation of poliovirus type 1(PV1). Methods We used cell culture, long‐overlapping RT‐PCR, and spot hybridization assays to verify and accurately locate the sites of action of ozone that cause PV1 inactivation. We also employed recombinant viral genome RNA infection models to confirm our observations. Results Our results indicated that ozone inactivated PV1 primarily by disrupting the 5′-non‐coding region(5′‐NCR) of the PV1 genome. Further study revealed that ozone specifically damaged the 80‐124 nucleotide(nt) region in the 5′-NCR. Recombinant viral genome RNA infection models confirmed that PV1 lacking this region was non‐infectious. Conclusion In this study, we not only elucidated the mechanisms by which ozone induces PV1 inactivation but also determined that the 80‐124 nt region in the 5′‐NCR is targeted by ozone to achieve this inactivation.

A case of adverse reactions of immune thrombocytopenic purpura caused by poliovirus vaccine

The child patient, male, 4 months and 16 days old, was vaccinated orally by Type I Type III Live Attenuated Oral Poliomyelitis Vaccine (human diploid cells) at 10:45 a.m. on June 1st of 2016 in Shaoxian Community Health Service Center of our hospital. Two hours after vaccination, the child patient showed erythema scattered on the upper of the left knee, on the right calf and on the abdomen. The forearm of the left upper limb was scattered with punctate rashes. He was admitted to Department of Pediatrics of our hospital at 12:32 on June 1st of 2016. The diagnosis was 'immune thrombocytopenic purpura'. After admission, the child patient received expert consultation and systematic treatment, consequently getting better.

Simultaneous detection of enterovirus-D68 and vaccine-related poliovirus 3 in the stool samples of a 5-month hospitalized child with acute respiratory disease:A case report

Human enterovirus(EV)infections can lead to various manifestations,with variable correlations between genotypes and symptoms.Human enterovirus D68(EV-D68)was considered to be associated with acute respiratory disease and acute flaccid myelitis.In this short report,both EV-D68 and poliovirus 3 were detected in the stool of a hospitalized 5-month child who presented with acute respiratory symptoms and who was recently vaccinated with oral polio vaccine(OPV),using a metatranscriptomic high-throughput sequencing method.The nearly full-length genome sequences with complete open reading frames of EV-D68 and poliovirus 3 were assembled.One previously-reported neurovirulence-related amino acid substitution(T860N)in the EV-D68 VP1 region was observed,but the patient showed no neurological symptoms.More attention should be paid to EV-D68,and continuous multiple syndrome-based surveillance on non-polio enterovirus is called for.

紫外线和次氯酸钠对Escherichia coli和Poliovirus的消毒作用

本研究选用大肠杆菌(Escherichia coli)和脊髓灰质炎病毒(poliovirus)分别作为典型的细菌和病毒,利用培养和定量PCR的检测技术,对比研究紫外线消毒和次氯酸钠消毒对细菌和病毒的作用特点.结果表明:脊髓灰质炎病毒比大肠杆菌更难被灭活,达到1-log所需的氯剂量分别为19.2 mg·L^(-1)·min和10.14 mg·L^(-1)·min;所需的紫外线剂量分别为6.37 m J·cm^(-2)和1.81 m J·cm^(-2).定量PCR方法检测大肠杆菌和脊髓灰质炎病毒达到1-log的核酸损伤所需的紫外线剂量和氯剂量要比培养法高出1~2数量级,紫外线消毒对脊髓灰质炎病毒的RNA损伤量明显大于对大肠杆菌的DNA损伤,病毒的单链RNA对紫外线的敏感性更强,该结果与培养法正好相反.达到1-log核酸损伤脊髓灰质炎病毒所需的紫外线剂量为135 m J·cm^(-2),大肠杆菌所需的剂量为270.3 m J·cm^(-2),核酸损伤需要更多的消毒剂量,可能由于消毒过程微生物进入活性但处于非可培养状态(VBNC),以及灭活对微生物其他分子的损伤和微生物死后核酸的持续性.

Polio eradication surveillance in Sri Lanka,2019-2023

Objective:To evaluate the polio laboratory surveillance carried out from January,2019 to May,2023 by the Polio Regional Reference Laboratory,Sri Lanka.Methods:This retrospective study analyzed all stool samples received under the acute flaccid paralysis(AFP)and immunodeficient vaccine-derived poliovirus(VDPV)surveillance at Polio Regional Reference Laboratory,Sri Lanka from January,2019 to May,2023.The results of the testing methodologies were extracted from the laboratory data system,i.e.,poliovirus virus isolation,intra-typic differentiation/VDPV real time reverse transcriptase polymerase chain reaction(ITD/VDPV rRTPCR)and sequencing,along with the data on timing of reporting results,stool adequacy and socio-demographics.Data was analyzed using descriptive statistics.Results:A total of 2141 stool samples from 1644 cases were received for AFP surveillance from Sri Lanka(93.61%),Maldives(1.52%),and immunodeficient VDPV(4.86%)surveillance.Both polioviruses(19/1644,1.15%)and non-polio enteroviruses(73/1644,4.44%)were isolated,while Sabin-like 3 virus was detected in majority(12/19,63.15%)among the poliovirus isolated.Wild polioviruses or circulating VDPVs were not detected among the cases.During all years of the study,the non-polio AFP detection rate was>1/100000 in children aged less than 15 years,whereas stool adequacy rate was>80%.All results were reported within 14 days of receipt,ensuring timely reporting as per global guidelines.Conclusions:The Polio Regional Reference Laboratory,Sri Lanka plays a vital role in maintaining the polio-free status in the country through its robust laboratory surveillance,while adhering to the surveillance indicators.Non-detection of wild polioviruses and circulating VDPV during the study period reinforces the polio-free status in the country.

Type I vaccine-derived polioviruses in China from 1995 to 2019

A nation-wide case surveillance was conducted in China since 1995 for the objective of identifying acute flaccid paralysis(AFP)in children so that potential wild polioviruses and vaccine-derived poliovirus(VDPV)could be identified on time.Two outbreaks associated with type I circulating VDPVs,eight native independent type I ambiguous VDPVs(aVDPV),and one imported aVDPV were identified during the AFP case surveillance in China from 1995 to 2019.The VP1 coding region of the Chinese type I VDPVs differed from the polio vaccine strain by 1.00%–3.75%(9–34 substitutions in 906 nucleotides).Most of the Chinese type I VDPV strains shared 4 amino acid substitutions in the neutralizing antigenic(NAg)sites:3 located at the BC loop,which formed the NAg site 1,and another at NAg site 3a.All of the Chinese type I VDPVs identified during the AFP case surveillance were young VDPVs,which indicated a limited viral replication resulted from the administration of the initiating oral polio vaccine(OPV)dose.VDPVs can emerge and spread in isolated communities with immunity gaps and the circulation ceases following a mass immunization with OPV.As such,high-quality surveillance permitted very early detection and response and it played a key role in stalling the widespread circulation of the emergent cVDPV strains in China.

Epidemiological survey and genetic characterization of type 3 vaccine-derived poliovirus isolated from a patient with four doses of inactivated polio vaccine in Henan Province,China

Background:Vaccine-derived poliovirus(VDPV)is a potential threat to polio eradication because they can reintroduce into the general population and cause paralytic polio outbreaks,a phenomenon that has recently emerged as a prominent public health concern at the end of global polio eradication.This study aimed to describe the epidemiology and genetic characteristics of the frst VDPV identifed from a patient with acute faccid paralysis(AFP),with four doses of inactivated polio vaccine immunization in Henan Province,China in 2017.Methods:The patient was diagnosed with type 3 VDPV.Subsequently,a series of epidemiological approaches was implemented,including a retrospective search of AFP cases,rate of vaccination assessment,study of contacts,and supplementary immunization activities.Fecal samples were collected,viral isolation was performed,and the viral isolates were characterized using full-length genomic sequencing and bioinformatic analysis.Results:Phylogenetic analysis showed that the viral isolates from the patient were diferent from other reported genetic clusters of type 3 VDPV worldwide.They were identifed as a Sabin 3/Sabin 1 recombinant VDPV with a crossover site in the P2 region.Nucleotide substitutions,including U→C(472)and C→U(2493),have been identifed,both of which are frequently observed as reversion mutations in neurovirulent type 3 poliovirus.A unique aspect of this case is that the patient had been vaccinated with four doses of inactive polio vaccine,and the serum neutralizing antibody for Sabin types 1 and 3 were 1∶16 and 1∶512,respectively.Thus,the patient was speculated to have been infected with type 3 VDPV,and the virus continued to replicate and be excreted for at least 41 d.Conclusions:The existence of this kind of virus in human population is a serious risk and poses a severe challenge in maintaining a polio-free status in China.To the best of our knowledge,this is the frst report of VDPV identifed in the Henan province of China.Our results highlight the importance of maintaining a high-level vaccination rate and highly sensitive AFP case surveillance system in intercepting VDPV transmission.

Corrigendum to“Silent circulation of poliovirus in small populations”[Infectious Disease Modeling 2(2017)431e440]

An error in a previous publication in the calculation of the average age at first infection for the model is corrected here.The average age at first infection for the effective contact rates used to generate the data ranges from 1.2 to 3.3 years of age instead of 3e5 years of age as advertised in the previous version of the paper.This change has an effect on the force of infection generated by this model.In this corrigendum,we demonstrate the correct method to calculate the average age at first infection for the model.We compare the forces of infection that correspond to these ages in our model with the forces of infection in other endemic populations.We show that the modified age range corresponds to forces of infection which are higher than those that are known to exist in historical studies of polioendemic regions.Thus,the results in the paper have limited applicability to real-world endemic situations.

Silent circulation of poliovirus in small populations

Background:Small populations that have been isolated by conflict make vaccination and surveillance difficult,threatening polio eradication.Silent circulation is caused by asymptomatic infections.It is currently not clear whether the dynamics of waning immunity also influence the risk of silent circulation in the absence of vaccination.Such circulation can,nevertheless,be present following a declaration of elimination as a result of inadequate acute flaccid paralysis surveillance(AFPS)or environmental surveillance(ES).Methods:We have constructed a stochastic model to understand how stochastic effects alter the ability of small populations to sustain virus circulation in the absence of vaccination.We analyzed how the stochastic process determinants of the duration of silent circulation that could have been detected by ES were affected by R0,waning dynamics,population size,and AFPS sensitivity in a discrete individual stochastic model with homogeneous contagiousness and random mixing.We measured the duration of silent circulation both by the interval between detected acute flaccid paralysis(AFP)cases and the duration of circulation until elimination.Results:As R0 increased and population size increased,the interval between detected AFP cases and the duration of circulation until elimination increased.As AFPS detection rates decreased,the interval between detected AFP cases increased.There was up to a 22%chance of silent circulation lasting for more than 3 years with 100%AFP detection.The duration of silent circulation was not affected by the waning immunity dynamics.Conclusion:We demonstrated that small populations have the potential to sustain prolonged silent circulation.Surveillance in these areas should be intensified before declaring elimination.To further validate these conclusions,it is necessary to realistically relax the simplifying assumptions about mixing and waning.

天然砂与修饰砂对病毒的吸附与去除

分别在不同pH、含有不同金属阳离子及腐殖酸的脱氯自来水与蒸馏水中,研究了砂与金属氢氧化物修饰砂吸附与去除Polivirus 1(PV1)和Bacteroides fragilis phage(B.fp)的不同效果。结果显示,天然砂吸附病毒效率随水体pH的降低而增加,但当砂表面经氢氧化铝、氢氧化铁沉积修饰后,却在中性pH具有较高的吸附率。金属阳离子可促进天然砂吸附病毒,并随其浓度和价态的增加而增加,但对修饰砂作用不明显。腐殖酸对砂及修饰砂吸附病毒的影响也不同,修饰砂吸附病毒不受腐殖酸的存在及其浓度影响,而天然砂会因腐殖酸的存在及其浓度的提高而降低吸附病毒效率。在任一实验条件下,砂与修饰砂在自来水中的吸附病毒效率高于在蒸馏水中的吸附效率,扫描电镜观察显示砂与修饰砂具有明显不同的表面结构特征,这是两者具有不同吸附效率的基础。从砂与修饰砂吸附PV1的效率高于B.fp的现象说明B.fp是一个更为合适的病毒去除指示生物。本实验结果表明了金属氢氧化物修饰砂可为传统的净水工艺提供高效的病毒去除过滤介质与途径。

中国首例iVDPVs病例粪便标本中病毒血清型分布和Ⅲ型iVDPVs VP1区基因特征

分析中国首例免疫缺陷疫曲衍生脊髓灰质炎病毒（immunodeficient vaccine-derived polioviruses，iVDPVs）急性弛缓性麻痹（acute flaccid paralysis，AFP）病例（实验室编号为9230）12份便标本中病毒血清型分布和分离物中Ⅲ型VP1区的基因特征。31个省的疾病预防控制中心脊髓灰质炎（脊灰）实验室网络，在2005年采用细胞培养、病毒分离和微量中和试验从5231例AFP病例中的293例的便标本中分离到脊灰病毒，其中从1例编号为9230的AFP病例发病2～150天的12份便标本中分离到17株脊灰病毒株，包括Ⅱ型12株，Ⅲ型5株。用PCR-RFLP和ELISA两种方法对送检的293例AFP病例中分离的病毒进行型内鉴定，VP1区序列测定和分析发现：从9230号病例粪便标本中分离的12株Ⅱ型为混合不同变异数目的Ⅱ型iVDPVs，5株Ⅲ型病毒为单一Ⅲ型iVDPVs；除9230号病例外未发现其它iVDPVs或疫苗衍生脊灰病毒（vaccine-derived polioviruses，VDPVs）。5株Ⅲ型iVDPVs的VP1基因和SabinⅢ相比有22～24个碱基突变，同源性为97．33％～97．56％，是中国至今发现变异最大的Ⅲ型VDPVs。9230号病例临床诊断为X-连锁低／无丙种球蛋白血症，是在中国首次发现的iVDPVs病例，该病例的病毒分离物中同时存在Ⅱ型和Ⅲ型iVDPVs，Ⅲ型iVDPVs在患者体内至少复制2．5年以上，iVDPVs病例的持续排毒已经给中国维持无脊灰状态提山了新的挑战。

急性弛缓性麻痹病例中Ⅱ型脊髓灰质炎疫苗病毒变异株基因特征分析

研究Ⅱ型脊髓灰质炎（脊灰）疫苗变异株的基因特征，为我国使用口服脊灰减毒活疫苗／脊灰灭活疫苗使用策略，维持无脊灰状态和全球最终消灭脊灰提供科学依据。根据型内鉴定的检测结果，从2000-2001年AFP病例分离到的Ⅱ型脊灰疫苗变异株中选取有聚集性的5株病毒进行全基因组序列测定（贵州省3株、山东省2株），并进行核苷酸、氨基酸同源性分析。贵州省3株病毒全基因组序列完全一致，但与SabinⅢ型病毒发生重组，重组区域在3A区（nt5343-5353）；与疫苗株相比，Ⅱ型区域变异10个碱基，其中VP1区变异4个，与SabinⅡ型株核苷酸同源性为99．56％，氨基酸同源性99．34％；Ⅲ型区域变异9个碱基。山东省2株病毒全基因序列共享16个突变位点，没有发生重组，与SabinⅡ型株相比，VP1区分别变异7个和4个碱基，核苷酸同源性分别为99．22％和99．56％，氨基酸同源性分别为99．0％和99．67％。上述5株病毒在重要的减毒位点nt481、nt2909均发生突变。此研究中5株病毒分属于两个不同的传播链，但是共享nt481、nt2909、nt2992三个突变位点，这3个突变位点不在重组区域内，他们的共同作用可能是影响病毒传播力的重要因素，但目前尚无证据证明脊灰疫苗病毒型间重组会增加病毒的毒力及传播力。

我国首例iVDPV病例Ⅱ型脊髓灰质炎病毒分离株的基因特征

对分离于我国首例iVDPV病例的Ⅱ型脊髓灰质炎病毒分离株的基因特征进行了研究。随机选择CHN9230-F3-Ⅱ株为研究对象,将其VP1区RT-PCR产物连接到T载体上进行克隆,随机挑选45个阳性克隆进行序列测定后获得45条VP1区核苷酸序列,这45条序列的VP1基因与昆明Ⅱ型疫苗株VP1基因差异13-24个核苷酸,变异率为1.44%-2.66%。45条序列在同源进化树图上分为3组,但都来源于CHN9230-F3-Ⅱ株,组成以优势株为主的相关突变株的病毒群,是典型的居群样存在形式。经RT-PCR后直接进行序列测定,并根据序列图中优势峰判读结果得到的CHN9230-F3-Ⅱ株核苷酸序列位于序列数量最多的第2组中,然而没有任何一条序列与之完全相同,说明它可能并不能代表具体的某一种序列,而只能是代表主序列具有的一般特征。3个组中的核苷酸序列与Ⅱ型疫苗株相比平均变异率分别为97.50%、97.93%和98.31%,根据脊灰病毒的进化率和3个组VP1区核苷酸序列的变异率推测,患者共5次服脊灰减毒活疫苗（OPV）史中的前3次OPV中的Ⅱ型疫苗病毒存活下来,依照疫苗接种顺序,分别形成了第1组、第2组和第3组的病毒居群样存在形式。我国Ⅱ型iVDPV以复杂的居群样形式存在,由于其进化速率较快并且感染了免疫缺陷患者,使其在该患者体内形成了持续性感染,它已经并可能将在更长的时间内在患者体内持续存在,一旦将来我国停止使用OPV后,iVDPV病例长期持续向外环境中排毒将对我国“维持无脊灰”带来严峻的挑战。

贵州省贞丰县疫苗衍生脊髓灰质炎病毒循环的病毒学分析

为及时发现和阻断疫苗衍生脊髓灰质炎(脊灰)病毒(vaccine-derived polioviruses, VDPVs)循环、脊灰野病毒的输入和能够引起临床脊灰的其它脊灰疫苗相关病毒,做好贵州省无脊灰状态下脊灰病毒学监测工作,采用病毒分离、鉴定与核苷酸序列测定和分析方法,对贵州省贞丰县及周围10个县2003～2004年报告的急性弛缓性麻痹(AFP)病例及2004年接触者粪便标本的病毒学监测的结果进行了分析. 对收集到的105例AFP病例和47例密切接触者的278份便标本进行了病毒学监测,结果从66例中共分离到肠道病毒(EV)66株,阳性率为43.4%,其中脊灰病毒(PV)29例,分离率为19.1%,非脊灰肠道病毒(NPEV)37例,分离率为24.3%.29例PV经中国疾病预防控制中心病毒病预防控制所国家脊灰实验室鉴定,24例为疫苗相似株,5例为脊灰Ⅰ型VDPVs,这5例均为2004年从贞丰县所分离到.贞丰县及周围县EV阳性检出率(43.4%)高于2003～2004年全省水平(22.9%～24.6%),2004年PV分离率比2003年高达2.6倍,29株PV中单个Ⅰ型占34.5%,明显高于往年(2000～2002年全省平均4.1%).本研究提示,Ⅰ型VDPVs在贞丰县引起了循环(cVDPVs),通过口服脊灰疫苗强化免疫已经阻断cVDPVs的传播.人群中PV和NPEV带毒率明显增高,非VDPVs引起的临床符合脊灰病例不容忽视;应加强脊灰病毒学监测数据的分析和早期疫情预警工作.

福建省脊髓灰质炎病毒分子流行病学研究

目的对福建省急性弛缓性麻痹（AFP）病例中分离的脊髓灰质炎病毒进行分子流行病学研究。方法用RT-PCR法扩增目的基因片段，通过核酸序列分析仪进行测序，将基因序列提交到美国国家生物技术信息中心（NCBI）GenBank上进行比对．并构建基因树。结果福建省1999～2002年分离到脊灰病毒5株，为Ⅱ型与Ⅲ型的疫苗重组。序列分析表明．福建省AFP病例中分离到的5株脊髓灰质炎病毒株VPI区与标准疫苗株的同源性高达99％以上．变异程度不大，与攀伎花市造成流行的脊灰病毒株差异也不大。同时发现，Fj-4，Fj-52株病毒为同一毒株。结论福建省在1999～2000年曾经出现过疫苗重组株，其中有一种毒株已在人群中循环，并引发2例病例。目前我国已进入无脊灰状态．仍采用减毒活疫苗进行免疫要注意脊髓灰质炎疫苗衍生株（VDPV）的流行。运用分子流行病学方法可以为适时调整免疫策略提供支持。

急性弛缓性麻痹聚集病例病原毒力和分子特征分析

为探索脊灰病毒型内重组、位点突变等分子特征与神经毒力的关系,对2002年6月四川省攀枝花地区发生的急性弛缓性麻痹(acute flaccid paralysis,AFP)聚集病例的分离病毒株进行了转基因小鼠(PVR-Tg21 mice)神经毒力实验和全基因组核苷酸序列测定。结果显示:所测4株分离病毒(均为Ⅱ型脊灰病毒)神经毒力没有明显升高。4株病毒基因全长都是7 439bp,编码区翻译的氨基酸全长2 207aa。4株病毒的VP1区核苷酸序列完全相同。6208和6235c两株病毒是由Ⅱ型和Ⅲ型脊灰病毒在3A区重组而来,6209和6236两株病毒是由Ⅱ型和Ⅰ型脊灰病毒在2C区重组而来。4株病毒在5'非编码区nt481和VP1区的nt2 909两个强减毒位点都发生回复突变,6209和6236两株病毒重组的SabinⅠ的重要减毒位点nt6 203亦发生回复突变。结合神经毒力实验和序列分析结果可以确定脊灰病毒的型别间的重组与神经毒力没有直接关系,同时可以推论SabinⅢ的nt5 832,SabinⅡ的nt1 450和nt2 386这3个位点可能是毒力相关位点。