| 1.Background&ObjectiveSince the implementation of the polio eradication plan in 1988,the incidence of poliomyelitis decreased significantly,and the number of popular countries with poliovirus epidemics gradually decreased.The world has entered the post polio Era.Although OPV plays a vital role in global control of polio process,the occurrence of vaccine-associated paralytic poliomyelitis(VAPP)and the acute flaccid paralysis(AFP)caused by vaccine-derived polio viruses(VDPV)becoming a prominent problem to be solved in the post polio Era.It is the most effective way to reduce and control VAPP and VDPV by using Inactivated poliovirus containing vaccine(IPCV)substitute for oral poliomyelitis attenuated live vaccine(OPV).In 2012,the World Health Organization(WHO)formulated the Polio Eradication and Endgame Strategic Plan 2013-2018 in order to eliminate all polio cases,including VAPP.This plan includes the introduction of at least one dose of inactivate polio vaccine(IPV)into routine immunization schedules based on children had a high PV vaccination rate after the global poliovirus transmission blocked worldwide.In 2009 and 2011,imported IPV and DTaP-IPV/Hib were licensed respectively and made available in China as private-sector,parent-pay vaccines.Although IPCV was made available in China,utilization rate was low and far behind the developed countries which had adopted the IPCV into their national immunization programs.In May 1,2016,China had adjusted the PV immunization strategy in accordance with its national conditions and adopted the first dose of IPV into the expanded program on Immunization(EPI)synchronize with more than 150 countries in the world.The immunization procedure was changed from 4 doses of trivalent OPV(tOPV)to 1 doses of IPV and 3 doses of bivalent OPV(bOPV)that was an important event in China’s immunization planning policy and may had far-reaching effects on the vaccination behavior characteristics of children.This paper analyzed vaccination behavior characteristics of PV among children born from 2008 to 2014 in Yinzhou district to master the PV vaccination rate,the IPCV substitution rate and the PV vaccination schedules proportions before adjusting the polio immunization strategy and provide baseline data for evaluating the impacts of PV immunization strategy adjustment.Besides,the change of polio vaccination behavior characteristics of PV among children were compared and analyzed before and after adjustment of immunization strategy to evaluate the effects of immunization strategy adjustment on PV vaccination behavior of children,to explore the related factors of the adjustment effect of immunization strategy,and propose suitable measures for promoting the positive impact of adjustment of immunization strategy.2.Materials&MethodsAll PV vaccination information of children born from 2008 to 2014 in Yinzhou district was exported from Ningbo Children’s Immunization Information Administration System into Microsoft Access In December 31,2015.Using descriptive epidemiogical method to gather statistics description in different household registrations and different residential areas children’s vaccination behavior characteristics of PV.2001 infants aged 5-7 months old were surveyed in April 30,2016 before the adjustment in November 30,2016 and 2005 infants surveyed in November 30,2016 after the adjustment in Yinzhou district including sociological characteristics such as gender,age,current address,household registration address,household registration type and PV vaccination status of primary immunization such as PV1 and PV1-3 vaccination rata,IPCV1 and IPCV1-3 substitution vaccination rata,PV1 and PV1-3 vaccination schedules proportions.The surveys database were built by Excel 2010 software and analyzed by SPSS 19.0 in single factor and Logistic regression analysis.3.Research Results3.1 Vaccination Behavior Characteristics of Poliovirus Vaccine among Children in Yinzhou DistrictThere were 125555 infants born from 2008 to 2014 in Yinzhou district.The coverage of PV1 and PV1-3 were 99.99%and 99.92%.The substitution rate of IPCV1 for OPV1 among children vaccinated with PV1 was 17.29%.The substitution rates of IPCV1 of children in different ages were between 0.16%to 43.78%,and decreased with age with significantly difference(X2=21683.81,P<0.001).There were statistical difference of substitution rates of ICV1 among children with different household registrations,and children living in different residential areas(P<0.05).16.42%children vaccinated with PV in a full primary immunization were vaccinated with IPCV1-3 substituting for OPV1-3.The highest substitution rates of IPCV1-3 of children was 42.28%in 2014 and the lowest was 0.08%in 2009.The substitution rates of IPCV1-3 decreased with age(x2=21 039.53,P<0.001).Multivariate analysis showed that the substitution rates of IPCV1-3 were higher among local children than among migrant children(OR=3.22,95%CI=3.11-3.34),in urban areas than in rural areas(OR=1.31,95%CI=1.26-1.36),and in high developed areas(OR=1.09,95%CI= 1.03-1.17)or in medium developed areas(OR=1.41,95%CI=1.32～1.51)than in low developed areas.Children born in 2011 to 2014 chose OPV,IPV and DTaP-IPV/Hib for PV1 accounted for 72.10%,16.30%and 11.59%,respectively.The O-O-O(all 3 doses were given with OPV)type was the mainly schedule accounted for 71.85%.Children chose I-I-I(all 3 doses were given with IPV)and D-D-D(all 3 doses were given with DTaP-IPV/Hib)schedules as the mainly substitution types accounted for 53.35%and 40.56%.3.1 Impacts of Immunization Strategy Adjustment on Vaccination Behavior of Poliovirus Vaccine among Children in Yinzhou DistrictMultivariate analysis showed that the immunization strategy adjustment affected the PV1-3 vaccination rate(OR=1.35,95%CI=1.07～1.70),IPCV1 substitution rate(OR=21.951,95%CI=17.776～27.107),IPCV1-3 substitution rate(OR=0.638,95%CI=0.552～0.737),PV1 and PV1-3 vaccination schedules proportion(P<0.001),but no effect on PV1 vaccination rate(OR=1.98,95%CI=0.96-4.07)in children after controlled factors of age,sex,household registration,urban and rural areas and regional economic level.Based on the multiple comparison,the vaccination proportions of IPV1 and DTaP-IPV/Hib1 for PV1 were increased but OPV’1 was decreased after the adjustment with significantly difference(P<0.017).The vaccination proportions of I-O-O,D-D-D and other sequential schedules for PV1-3 were increased but O-O-O,I-I-I and I-I-O schedules’ were decreased,all demonstrated statistically significant(P<0.009)when compared with before adjustment.Research ConclusionsThe coverage of PV1 and PV1-3 maintained at a high level and reached the required PV vaccination rate level of IPV-OPV sequential immunization strategy adjustment in Yinzhou district.Although Yinzhou children’s IPCV1 and IPCV1-3 substitution rates were low and still far behind the developed countries,both were rising in recent years.It’s just that there were various kinds of PV vaccination schedules.On the purpose of eliminating the ultimate goal of all poliomyelitis cases including VAPP,the work of IPCV substitution vaccination to suitable children should be strengthened.Health education should be conducted to help parents to choose an appropriate immunization schedule for their children.The PV immunization strategy adjustment improved the substitution vaccination rate of IPCV1 of children,but reduced the substitution vaccination rate of IPCV1-3 that may partially offset the positive benefits of IPCV1’s increasing.From the perspective of macro policy,the government should assess the impact of strategy adjustment on vaccine demand,supply,and vaccination services before the adjustment of immunization strategy and make adequate preparations to play the health benefits of the policy to the public. |
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