Study design and intervention package
Our study was an intervention trail with a pre- and post-test design. The intervention package was conducted for 32 months from October 2011 to May 2014. A pre-intervention investigation was conducted in September 2011 and a post-intervention investigation in June 2014.
Yiwu comprises 13 towns and each town has a health facility. Routine immunization services were provided by fixed immunization clinic in each health facility (outreach service was not allowed since 1998). All the 13 towns were selected as the unit of intervention, namely, the interventions were implemented throughout the entire town.
The EPI intervention package implemented in this study included following aspects:
Extending the EPI service time and increasing the frequency of vaccination service: the EPI service was provided from 8:00 am to 11:00 am once per week (on Wednesday) in every immunization clinics before this study. During the study, the service time of immunization clinics and the frequency of service were extended to allow migrant caregivers more time to attend.
Training program for vaccinators: a two days refreshing training was provided to all the vaccinators from 13 immunization clinics (107 vaccinators in total) in October 2011. The training program was designed by expert panel on immunization of Zhejiang provincial center for disease control and prevention (CDC). The training content focused on valid doses and management of Adverse Event Following Immunization (AEFI). A combination of training methods including lecture, group discussion, PowerPoint presentation and role-paly was applied. All the vaccinators completed the pre- and post- training questionnaires (see the Additional file 1: Table s1) to evaluate changes on immunization knowledge.
Developing a screening tool (see the Additional file 1: Figure s1) to identify vaccination demands among migrant clinic attendants: a screening tool was developed by Zhejiang provincial CDC and Yiwu CDC to check the immunization status of migrant children when their mothers visited a health facility for child care service or other medical service. If a migrant child required vaccination, it was provided immediately at the immunization clinic if available, otherwise, the child was appointed to the next nearest vaccination session. This intervention was implemented by the general practitioners in health facilities.
Social mobilization for immunization: Yiwu CDC formed social mobilization teams for each town, which consisted of general practitioner in health facilities, rental house owners, caregivers of fully immunized children, teachers of daycare centers/kindergartens/primary schools. The responsibilities of these teams were to assist in ensuring the registration of the EPI target migrant children, to disseminate EPI knowledge to migrants through booklets or pictorial cards, and to mobilize migrants to participate in the vaccination on their own initiatives. A half day orientation, led by expert panel on immunization of Zhejiang provincial CDC, was held for social mobilization team members. Monthly meetings were held with team members to review, praise and motivate their previous effort by Yiwu CDC.
In this study, migrants referred to people living in an area without a household registration card issued by public security bureau of their current living areas. We determined the immigration status of children or their caregivers by checking their Resident ID Card or asking their residence address. The study population included migrant children aged 1–4 years (children born from 1 September 2007 to 31 August 2010 were selected for the pre-intervention investigation and children born from 1 June 2010 to 31 May 2013 were selected for the post-intervention investigation) and their mothers, vaccinators from 13 immunization clinics. Migrant children who had lived in the surveyed areas continuously for more than one month were included in this study. We documented the date of the last immigration of the surveyed migrant children, then we calculated the length of time for continuously living in the surveyed areas.
First, the proportion of migrant people of each villages or communities were calculated based on the data provided by Bureau of Statistics of Yiwu. Second, villages or communities where migrants accounted for more than half of the total population were selected as investigation sites. Finally, 56 investigation sites for the pre-intervention investigation and 57 investigation sites for the post-intervention investigation were selected, respectively. Second, we calculated the sample size by the method of simple random sampling , setting an assumption coverage of 85 %, a significance level of 0.05, a design effect level of 2 and a desired precision of 3 % for the pre-investigation. For the post-investigation, the desired precision increased into 5 %. The final sample size were 1120 (20 children per cluster for 56 clusters) and 399 (7 children per cluster for 57 clusters) for the pre- and post-investigation, respectively.
Data were obtained from three sources: (1) random sample investigation to evaluate the vaccination coverage, (2) vaccination service statistics of immunization clinics, and (3) qualitative components from vaccinators and mothers of migrant children. These data were collected before and after the implementation of the EPI intervention package. Supervisors from Zhejiang provincial CDC were required to review all these data for logistic errors or blanks. All these errors should be addressed through reinvestigation when needed.
Random sampling investigation
Both the pre- and the post- intervention investigation were implemented in 2 weeks before and after the intervention period immediately. We got household list of every investigation site from local administrative office and used the random number to select one household as the first one to be investigated. If there was more than one eligible child in a household, the child whose birthday was the closest to the survey day was investigated. After found the first eligible child, we continued choosing subsequent household located at the right of the previous one until all the eligible children for each investigation site were investigated. A standardized, pretested questionnaire (see the Additional file 1: Table s2) was used for face-to-face interviews for both the pre- and the post- intervention investigation. Demographic details, such as child gender, number of children in family, mother’s age, mother’s education level, child’s birth place and monthly household income per capita, and mother’s knowledge on immunization were collected. Children’s vaccination status were confirmed by checking the immunization card kept by caregivers or immunization records kept by immunization clinics. Only written vaccination records were applied to avoid inaccuracies or recall bias. Twenty-six staff of Yiwu CDC were selected and trained as interviewers in this study. A training meeting was held for all the interviewers to ensure they were familiar with the questionnaire and investigation skill for sensitive question. Public health liaisons (some private doctors recruited by village level administration) of each investigation site were invited as guiders for help.
Vaccination service statistics
Vaccination service statistics (the EPI service time, the frequency of the vaccination service, number of attendance of the vaccination session) were collected from each immunization clinic and reviewed to ascertain the changes in performance of vaccination service. The effect of training was assessed through the changes in the incidence of invalid doses/AEFI among migrant children, and the knowledge level on immunization of vaccinators. Data on using the screening tool (number screened for immunization demands, number of demands identified, number followed up to ascertain its outcome) were also collected. Furthermore, data or field notes on the number of notification for registration or vaccination, social mobilization for immunization were also documented. All these data were collected by staff of Yiwu CDC.
Quality components from mothers of migrant children and vaccinators
Experts on immunization from Zhejiang provincial CDC organized a group discussion with mothers of migrant children. The mothers whose children were fully immunized in the post-intervention investigation were randomly selected. The discussion focused on the reasons for fully immunization, timely vaccination, and challenges they faced in existing vaccination service delivery system. Experts on immunization from Zhejiang provincial CDC also held a review meeting with 13 vaccinators (one vaccinator from each immunization clinic) after intervention to collect their perceptions on the EPI intervention package, and challenges faced in implementation.
Quantitative data were analyzed with the SPSS version 13.0 software. The analysis of quantitative data was based on a “before and after” evaluation. Pearson χ2 test was adopted to compare the difference in specific vaccination coverage and mothers’ demographic categorical variables before and after the implementation of the EPI intervention package. A P < 0.05 was considered to be significant. Qualitative data collected through observation, group discussion and review meeting were first documented, then coded, categorized and abstracted manually by carefully reading field notes, and finally analyzed using content analysis.
This study was approved by the Ethical Review Board of Zhejiang Provincial Center for Disease Control and Prevention. In each random sampling survey, the informed consent form on behalf of children and their caregivers enrolled was discussed with children’ s caregivers, and signed by one of them once there was a decision to participate.