| Objective: To analyze the changes of the epidemiological characteristics of acute flaccid paralysis(AFP)cases in Hebei Province,before and after the switching of polio vaccination schedule;thus evaluating its effects and providing scientific basis for elimination of poliomyelitis.Methods:1.Descriptive epidemiological method was used to analyze the epidemiological and pathogenic characteristics of AFP cases reported by AFP surveillance system two years before and after the switching of polio vaccine schedule(May 2014-April 2016 and May 2016-April 2018)in Hebei Province.2.Human rhabdomyosarcoma cell(RD cell)and mouse lung cell transfected with the gene for human cell-surface receptor specific for poliovirus(L20B cell)were used to isolate polio virus and positive cases were identified by real-time fluorescent quantitative RT-PCR for intratypic differention.The level of serum polio neutralizing antibody were determined by poliovirus neutralization test.3.Statistical tests were carried out by SPSS21.0 software: Chi-square test and Fisher's exact probability method were used to compare the difference of the rates and proportions,rank sum test was used to compare the distribution of ranked data,analysis of variance was used to analyze the level of serum polio neutralizing antibodies,all these were tested at the level of ?=0.05;multivariate logistic regression was used to analyze the risk factors.Results:1.Before and after the switching of polio vaccination schedule,652 and 633 AFP cases were reported in Hebei Province,with the reported incidence of 2.49/100,000 and 2.26/100,000 respectively(?2=2.903,P=0.088).2.The proportion of AFP cases aged 0-4 years before and after the switching was 63.50% and 54.98%,respectively(Z=-3.438,P=0.001).The sex ratio was 1.72:1 and 1.30:1,respectively(?2=5.886,P=0.015).The cases were scattering distributed in months and cities.Residual paralysis rates of AFP cases were 14.72% and 16.27% respectively(?2=0.588,P=0.443).3.Before the switching,there were 4 cases of VAPP and 1 case of VDPV reported,and after this switching,none was reported.4.Before and after the switching the positive isolation rates of polio virus were 2.91% and 1.26% respectively(?2=4.252,P=0.039).There were 7 and 5 PV1 strains,11 and 5 PV2 strains and 4 and 5 PV3 strains isolated respectively(P=0.010).The isolation rates of non-polio enteroviruses(NPEV)were 14.88% and 12.95% respectively(?2=0.002,P=0.960).5.From 2012 to 2016,the GMTs of polio virus neutralizing antibodies to type I,type II and type III polioviruses of children aged 0-2 years were 1:216.93,1:217.18 and 1:168.04,respectively;from 2017 to 2018,the GMTs of neutralizing antibodies to type I and type III polioviruses were 1:237.15 and 1:114.71 respectively;there were no significant differences in the GMTs of neutralizing antibodies to type I polioviruses(F=0.091,P=0.764)and type III polioviruses(F=0.687,P =0.408)before and after the switching.Conclusions:1.Epidemiological characteristics of AFP cases which had not changed after the switching of polio vaccination schedule include the reported incidence,seasonal and regional distribution,residual paralysis rate and GMTs of the polio virus neutralizing antibodies.2.Epidemiological characteristics of AFP cases which had changed after the switching of polio vaccination schedule include the reported incidence of VAPP and VDPV cases,isolation rate of positive PV from AFP cases. |
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