Coverage estimates and patterns of inactivated poliovirus vaccine (IPV) use prior to and during the polio eradication endgame, Jinan City, China, 2010–2015

ABSTRACT

Background: Use of inactivated poliovirus vaccine (IPV) in Jinan during the polio eradication endgame has not been previously documented. Two IPV-containing vaccines were made available as an option for Jinan parents in 2009. We describe coverage levels and patterns of use of IPV over time using data from the Jinan Childhood Immunization Information Management System (JNCIIMS).

Methods: Children born between January 2010 and December 2014 who were registered in JNCIIMS were included in this study. Vaccination records were obtained from JNCIIMS on April 30, 2015. JNCIIMS distinguishes among available poliovirus vaccines; doses administered data were used to describe IPV usage over time. We identified the polio vaccination sequences used by children in the 2012 and 2013 birth cohorts. Coverage estimates were analyzed by birth cohort and migration status. We developed 3 categories for analysis: “resident child,” “migrant child” and “other child” according to migration status.

Results: In total, 12,354 (11.7%) IPV, 5,893(5.6%) DTP-IPV-Hib vaccine and 87,054(82.7%) OPV doses were administered to children in the 2010 to 2014 birth cohorts. The proportion of children using an IPV-only schedule increased each year, consistent with the introduction of IPV that is called for by the Polio Eradication Endgame Strategic Plan 2013–2018. During this time, 4.7% children used a schedule containing both IPV and oral poliovirus vaccine (OPV). In the 2012 to 2013 birth cohorts, 14.4% children used an IPV-only schedule; 5.7% children used a sequential schedule, and 79.9% used OPV-only schedule. Use of IPV only schedules was higher among migrant children than among resident children. Among those sequential schedule using both IPV and OPV, 87.2% children used IPV for the first dose and 12.8% used OPV for the first dose.

Conclusions: JNCIIMS provided a mechanism for tracking IPV and OPV vaccination patterns, and showed areas in need of improvement. Ensuring appropriately sequenced IPV and OPV supports reduction of risk of vaccine associated paralytic polio.

KEYWORDS:

• coverage rate
• Inactivate polio vaccine
• sequential schedule

Introduction

In 2012, the Global Polio Eradication Initiative partners developed the Polio Eradication and Endgame Strategic Plan 2013–2018, which was subsequently approved by the World Health Assembly.¹ This plan includes the introduction of at least one dose of inactivate polio vaccine (IPV) into routine immunization schedules as a strategy to reduce risk from type 2 vaccine-derived polioviruses (VDPV2) following the withdrawal of Sabin type 2 strains from oral polio vaccine (OPV).² IPV provides a base of immunity that can be boosted with monovalent OPV2 in case of a VDPV2 outbreak. IPV induces long lasting immunity and does not cause vaccine-associated paralytic poliomyelitis (VAPP) or VDPVs.

In 2009, imported IPV-containing vaccines were licensed and made available in China as private-sector, parent-pay vaccines.³ IPV became available in Jinan in April of 2009. Although IPV was made available in China, utilization was low due to its high price. In contrast, OPV has always been provided at no charge to parents, regardless of socioeconomic status. Huizhou City in Guangdong Province introduced IPV into the management of the Expanded Program on Immunization making the vaccine available at no charge. However, in other cities IPV remained an option for parents to consider, although they would have to pay for the vaccine. Optional use of IPV has not been documented. We used data from the Jinan Childhood Immunization Information Management System (JNCIIMS) to describe polio vaccination coverage and patterns of use of IPV and OPV in order to provide baseline data and experience to inform national immunization strategies.

Results

In total, 105,301 doses of polio vaccine were administered to children in the 2010 to 2014 birth cohorts; 87,054 (82.7%) doses were OPV, 12,354 (11.7%) were IPV, and 5,893(5.6%) were DTP-IPV-Hib combined vaccine. Table 1 shows vaccine use by year. Table 2 shows use of different polio vaccination schedules by year of birth. Use of IPV-only schedules increased over time, but they were used less frequently than an OPV-only schedule and more frequently than sequential schedules.

Table 1. Different types of polio vaccine used by year of birth.

Type	2010	2011	2012	2013	2014	Total
OPV	16,760	18,712	16,967	16,127	18,488	87,054
IPV	375	830	1,966	3,693	5,490	12,354
DTP-IPV-Hib combined vaccine	19	53	866	1,765	3,190	5,893
Total	17,154	19,595	19,799	21,585	27,168	10,5301

Table 2. Polio vaccination schedules by year of birth.

	IPV only		Sequential schedule		OPV only		Total
Birth cohort	No. of children vaccinated	Percent (%)	No. of children vaccinated	Percent (%)	No. of children vaccinated	Percent (%)	No. of children vaccinated	Percent (%)
2010	347	0.4	2,025	2.5	79,892	97.1	82,264	100
2011	2,450	3.2	2,259	2.9	72,706	93.9	77,415	100
2012	9,181	10.1	4,271	4.7	77,675	85.2	91,127	100
2013	15,126	19.4	5,404	6.9	57,482	73.7	78,012	100
2014	25,880	24.4	6,308	5.9	74,053	69.7	106,241	100
Total	52,984	12.2	20,267	4.7	361,808	83.1	435,059	100

To ensure that children were old enough to have received at least 3 polio vaccine doses by April 30, 2015, we conducted analyses restricted to the 2012 and 2013 cohorts. Table 3 shows use of different schedules by birth cohort and by migration status for children in the 2012 and 2013 cohorts. Use of IPV only schedules was higher among migrant children than among resident children.

Table 3. Polio vaccination schedules by birth cohort and migration status.

	IPV only		Sequential schedule		OPV only		Total
Variant	Children vaccinated	(%)	Children vaccinated	(%)	Children vaccinated	(%)	Children vaccinated	(%)
Birth cohort
2012	9,181	10.1	4,271	4.7	77,675	85.2	91,127	100
2013	15,126	19.4	5,404	6.9	57,482	73.7	78,012	100
Migration Status
Resident	13,588	12.3	6,577	6.0	90,003	81.7	110,168	100
Migrant	9,369	18.8	2,694	5.4	37,886	75.8	49,949	100
Other	1,350	15.0	404	4.5	7,268	80.5	9,022	100
Total	24,307	14.4	9,675	5.7	135,157	79.9	169,139	100

Table 4 shows use of sequential schedules by the type of polio vaccine used for the first dose – IPV or OPV. For the 2012 and 2013 birth cohorts, 87.2% children used an IPV-first sequential schedule, with a higher percentage in the 2013 birth cohort; 77.2% of migrant children used an IPV-first sequential schedule, compared with 89.2% of resident children. Table 5 shows variants of sequential schedules for the 2012 and 2013 birth cohort children. Among children in these cohorts, 55.8% used an IPV-IPV-OPV sequential schedule, 28.8% used an IPV-OPV-OPV sequential schedule.

Table 4. IPV-first and OPV-first sequential schedule use among 2012–2013 cohort children.

	IPV-OPV sequential schedule		OPV-IPV sequential schedule		Total
Variant	Children vaccinated	(%)	Children vaccinated	(%)	Children vaccinated	(%)
Birth cohort
2012	3,560	83.4	711	16.6	4,271	100
2013	4,872	90.2	532	9.8	5,404	100
Migration Status
Resident	5,867	89.2	710	10.8	6,577	100
Migrant	312	77.2	92	22.8	404	100
Other	2,253	83.6	441	16.4	2,694	100
Total	8,432	87.2	1,243	12.8	9,675	100

Table 5. Sequential schedule variations for the 2012–2013 birth cohort children.

Sequence schedule	Children vaccinated	(%)
IPV-IPV-OPV	5398	55.8
IPV-OPV-OPV	2788	28.8
OPV-IPV-IPV	529	5.5
OPV-OPV-IPV	275	2.8
OPV-IPV-OPV	198	2.1
IPV-OPV-IPV	64	0.7
(DTP-IPV-Hib)-OPV-OPV	61	0.6
OPV-(DTP-IPV-Hib)-(DTP-IPV-Hib)	52	0.5
OPV-(DTP-IPV-Hib)-(DTP-IPV-Hib)-(DTP-IPV-Hib)	45	0.5
Others	265	2.7
Total	9675	100

Discussion

Our study took advantage of the Jinan Childhood Immunization Information Management System (CIIMS) to evaluate coverage and use of IPV in Jinan in the years prior to the nationwide introduction of IPV into China. Use of IPV-containing schedules increased from less than 3% the year after IPV became available in Jinan to approximately 30% 4 y later. Use of an all-OPV schedule decreased concomitantly.

We also showed that vaccination coverage levels for migrant children were lower than for resident children in the 2012 and 2013 birth cohorts. In these cohorts, 12.8% of children used an OPV-IPV sequential schedule, which provides less protection from VAPP than an IPV-first schedule.

A strength of our study is that it used JNCIIMS, which serves as the official vaccination record for children in Jinan. Because it is the official record, JNCIIMS is the most accurate method to evaluate and establish baseline coverage.^4,5 A second advantage of JNCIIMS is that it is considered as a census of all children <7 y in Jinan City, rather than a sample of the target population. A weakness is that JNCIIMS may underestimate coverage due to incomplete provider reporting. Children not captured by JNCIIMS may differ in their immunization status from children in JNCIIMS, but this should have minimal impact on coverage rates, as over 95% of children are registered in Jinan CIIMS. An advantage of our study is that we were able to determine trends in utilization of IPV-containing vaccines going into the early part of the Polio Eradication Endgame Strategic Plan 2013–2018. This information may help to predict IPV demand after the globally-synchronized switch from trivalent OPV to bivalent OPV and nationwide introduction of IPV.

Like other immunization information systems, the JNCIIMS platform is able to provide data to assess immunization coverage levels. In the United States, Shauer and colleagues estimated baseline childhood immunization rates using an immunization information system.⁵ Zhang and colleagues⁶ assessed the status of CIIMS in Shandong province, and they found that the CIIMS was in universal use in Jinan by the end of 2012. We found that polio vaccination coverage for migrant children was lower than for resident children in both 2012 and 2013 birth cohorts, which is consistent with previous research in China.⁷

Our study has program implications. The risk of VAPP is highest with the first dose of OPV in an all-OPV schedule. The rate of VAPP associated with the first dose of OPV has been shown to be approximately 1 case per 0.9 million doses, a 6.6-fold greater risk than that following exposure to subsequent doses of OPV.⁸ The introduction of inactivated poliovirus vaccines with enhanced potency⁹ has generated interest in sequential schedules with IPV given before OPV to reduce risk of VAPP.¹⁰ Our study showed that among children using a sequential schedule, 87.2% used IPV for first dose for 2012 and 2013 birth cohort; however, 12.8% child used a sequential schedule that started with OPV, which provide less protection from VAPP than an IPV-first schedule. Our findings support 2 recommendations. First, it is important to increase the basic immunization coverage rate of polio vaccine, especially among migrant children. Second, ensuring appropriately sequenced IPV and OPV supports reduction of risk of vaccine associated paralytic polio.

Methods

Demographic characteristics of children and their linked poliovirus vaccine doses administered were obtained from JNCIIMS, an immunization information system that has been in existence since 2004. JNCIIMS maintains official immunization data for children aged <7 y of age living in Jinan. It is an Internet-based, real-time, client-server application that is deployed in all immunization clinics under the authority of Jinan Municipal CDC.⁶ Immunization records for this study were obtained on April 30, 2015; we included children in the 2010 to 2014 birth cohorts. Each birth cohort consisted of children born between January 1 and December 31 of the birth cohort year.

Jinan CDC recommends a 4-dose IPV primary vaccination series given at 2, 3, 4 and 18 months of age for children with contraindications to OPV primarily children with immune deficiencies or who are on immunosuppressive drugs.³ Jinan adapted this guideline into a sequential IPV schedule as an option for families of healthy children to consider as an alternative to an all-OPV schedule.

We defined an IPV-only schedule a polio vaccination schedule consisting of only IPV-containing vaccines (standalone IPV or DTP-IPV-Hib combination vaccine), which were recommended for ages 2, 3, 4 and 18 months.

An OPV-only schedule consisted of OPV with no IPV-containing vaccine doses; recommended ages were 2, 3, and 4 months with a booster dose at 4 y of age. An IPV-OPV sequential schedule was defined as a mixed IPV and OPV schedule in which an IPV-containing vaccine was given as the first dose. Variants of the IPV-OPV sequential schedule were IPV-OPV-OPV-OPV, IPV-IPV-OPV-OPV, and IPV-IPV-IPV-OPV. An OPV-IPV sequential schedule was defined as a mixed OPV and IPV schedule in which OPV was given as the first dose. Variants of the OPV-IPV sequential schedule include OPV-IPV-IPV-IPV, OPV-OPV-IPV-IPV, and OPV-OPV-OPV-IPV. We also described use of mixed sequential schedules, for example, starting and ending with IPV but using OPV for doses 2 and 3.

Migration status was recorded in JNCIIMS as “migrant child from other country,” “migrant child from other province,” “migrant child from other municipalities in Shandong Province,” “migrant child from other district of Jinan city,” “resident child,” “temporary child,” or “other child.” We developed 3 categories for analysis: “resident child,” defined as children who lived in the district for more than 3 months; “migrant child,” consisting of the variants of migration status stated above who lived in the district for less than 3 months; and “other child,” as all other children. Children passing through Jinan who used the EPI clinic for a one-time vaccination were not included in our study.

Data analysis

Statistics Analysis System (SAS9.2) was used to edit the database by deleting duplicate records and records containing impossible values or that were missing vaccination records. Analyses were descriptive and consisted of counts, frequencies, and percentages.

Ethical considerations

This study was approved by the Institutional Ethics Committee of Jinan municipality Center for Disease Control and Prevention. All data were anonymized when exported from JNCIIMS and lacked personal identifying information.

Abbreviations

IP	=	Inactivate Polio Vaccine
OPV	=	Oral Polio Vaccine
VAPP	=	Vaccine-Associated Paralytic Poliomyelitis
VDPV	=	Vaccine-Derived Polioviruses
CIIMS	=	Childhood Immunization Information Management System

Disclosure of potential conflicts of interest

The authors declare no conflict of interest.

Acknowledgments

We would like to thank Zhijie An, Huilai Ma, Li Yan, Liu yan and Wang Liang for your critical support for this study. We thank Dr Lance Rodewald for critical support and review of the manuscript and response to the editor and reviewer comments.