Immunization status and risk factors of migrant children in densely populated areas of Beijing, China
Introduction
In the past decade, China had achieved remarkable economic growth through the development of market economy. Its GDP per capita more than doubled from $721 in 1995 [1] to $2006 in 2005 [2]. However, regional income imbalance remained large. In 2005, annual incomes per capita for urban and rural households in eastern regions were 55% and 71% higher than those in western regions [2]. These regional disparities have become a key driving force of the country's largest tide of internal migration in its history. According to China's Fifth Population Census in 2000, there were more than 121 million internal migrants [3]. “Migrants” referred to people living in places other than their hometowns but possessing no local household registration card (Hukou) of their current living address; whereas “registered people” were those residing in their hometowns and owning the local Hukou [4].
As a developed city in east areas in China, Beijing alone has attracted more than 2.5 million migrants in 2000 [4]. In 2005, the number of migrants in Beijing increased to 3.5 million [5]. According to official statistics [6], 78% migrants came to Beijing for work, 14% came just to be with their family members, and less than 10% came for other purposes. More than 90% migrants did not have their own houses in Beijing: 51% lived in houses rented from the registered people, and 42% lived in places provided by their employers. Due to high living cost in central Beijing, only 10% of migrants lived there despite its easy access to public transportation. In contrast, inner and outer suburban districts, providing better balance of living cost and public transportation availability, attracted 59% and 26% of migrants, respectively. The rest 5% migrants lived in the rural areas around Beijing. Apart from living cost and traffic conditions, social networks, such as kinship or friendship ties, of migrants could be another important reason for the uneven distribution of migrants. Their first residence places were largely predetermined by the location of their kin or friends [7]. Typically, migrants in central Beijing lived in storied buildings just like the registered people. These buildings provided good living conditions and had municipal sanitary system. In contrast, in most suburban areas, especially in towns and townships with high density of migrants, migrants lived in small single-storied dwellings (Pingfang) with poor ventilation that accommodated one entire family and had no in house hygiene facilities.
The problem of low immunization coverage of migrant children has long been recognized by Beijing government. Since the mid of the 1990s, migrant children have been covered in Beijing's Expanded Program of Immunization (EPI) and thus have access to the same free vaccine and vaccination services as those registered children. Migrant parents or caregivers have not been required to show their Temporary Residence Card (TRC) to have their children vaccinated, although TRC was issued by municipal government for every migrant aged 16 years or above.
To further improve vaccination coverage, vaccination clinics in towns and townships with less than 500 preschool migrant children have been required to conduct semi-annual supplementary immunization activities (SIAs) [8]. In towns and townships that had 500 or more preschool migrant children, SIAs have been required quarterly. During SIAs, healthcare workers made house-to-house visit within their catchment areas accompanied by local guides to identify incompletely vaccinated children, then immunized them in clinics‘. Migrant children in Beijing, therefore, enjoyed the same or easier access to routine immunization than the registered children.
In the national EPI evaluation conducted by China's Ministry of Health (MOH) in 2004, 93% children aged 1–3 years in Beijing completed the primary doses of Bacille Calmette Guerin (BCG), diphtheria, tetanus and pertussis combined vaccine (DTP), oral poliomyelitis vaccine (OPV), and Measles-containing vaccine (MCV) [9]. However, in towns and townships with more than 10,000 migrants, less than 80% children of 1–3 years completed those immunizations [10]. These towns and townships therefore were immunization pockets of need in Beijing. Due to much lower vaccination coverage of migrant children than of registered children (65% vs 96%) [10], interventions specially targeted at migrant children in these areas were greatly needed.
In developed countries, risk factors for undervaccination of children at low socioeconomic level were explored and effective strategies were implemented [11], [12]. But different from minorities or international immigrants in those researches [11], [12], most migrants in Beijing were the same nationality with registered people and came from undeveloped areas in China. No special religious beliefs existed among these migrants to prevent parents and caregivers from having their children vaccinated [13]. The immunization system in Beijing also differed from that in developed countries [14]: all children were vaccinated in public clinics which provided no medical services, and all EPI vaccines were purchased by municipal government and provided to registered and migrant children free of charge regardless of whether they had medical insurance. Thus risk factors for undervaccination of migrant children in Beijing may differ from that in developed countries, which would lead to different healthcare strategies. In some developing countries, researches [15] reported an association between migration and decreased immunization coverage. However, evaluation of age-appropriate vaccination coverage of migrants was very limited and risk factors from the perspective of immunization provision were rarely reported if not absence. Meanwhile, social networks of migrant parents and caregivers had been reported to have impact on migrant children's health in developing countries [16]. The association between those networks and vaccination coverage therefore might exist and should be considered when exploring risk factors for underimmunization of migrant children.
According to Beijing's immunization activity for OPV in April 2005 [17], above 80% pre-school migrant children lived in inner and outer suburban districts. In these districts, about 48% pre-school migrant children lived in 23 towns and townships out of the total 177 towns and townships. Each of these 23 towns and townships had more than 1500 pre-school migrant children and was called “densely populated areas” in our research. In these densely populated areas, migrant children less than 6 years accounted for 82–96% of the total pre-school children based on reported data from local immunization clinics, though no related official statistics could be acquired. Migrant families in these areas lived in low-quality Pingfang described previously and vaccination coverage of their children was considered to be low, which made them more susceptible to some vaccine-preventable diseases. In 2005, reported measles cases of pre-school migrant children in these areas accounted for 53% of the total cases at the same age in Beijing.
In 2005, a project financed by UNICEF was launched to explore effective strategies to improve immunization coverage of migrant children in their densely populated areas. Our survey was conducted to estimate the actual complete and age-appropriate immunization coverage of migrant children in project areas and determine risk factors.
Section snippets
Vaccination recommendations
Since 1978, BCG, DTP, OPV and MCV have been included in EPI in China. In 2002, hepatitis B vaccine (HepB) was introduced. Since then, no changes occurred in the national immunization schedule for primary doses of these five vaccines. Because BCG vaccine was administered in special immunization clinics in Beijing which were not covered by our survey, we evaluated immunization coverage for the other four vaccines. Table 1 shows national recommended ages for primary doses of these four vaccines.
Target population
Coverage of immunization status for each primary dose, each vaccine series and the 3:3:3:1 immunization series
Table 2 summarizes the weighted coverage and the weighted age-appropriate immunization rate of each primary dose of the studied four vaccines. For HepB, OPV, and DPT series, the weighted coverage decreased with doses. The coverage gap between the 1st dose and 3rd dose ranged from 4.0% for OPV series to 6.4% for HepB series. For each antigen, the weighted UTD immunization rate was above 83%, but the weighted age-appropriate immunization rates were much lower to 45.6%, 49.6%, 50.8% and 54.7% for
Discussion
The low immunization coverage of migrant children had been discussed in China [10], [22] and some other developing countries [15]. However, the low age-appropriate immunization rate of migrant children, which revealed substantial inequalities within a population [23], [24], [25], [26], was seldom reported and therefore did not attracted much attention of policymakers. We founded that although low immunization coverage of migrant children in their densely populated areas did not attain the MOH's
Conclusion
For the first time, to our knowledge, our findings demonstrated importance of age-appropriate immunization status of the 1st dose within the vaccine series among migrant children. It was imperative that we focused on substantially low age-appropriate immunization coverage and its risk factors of migrant children in their densely populate areas. Future intervention in Beijing should be primarily aimed at the child with one or more characteristics as follows: aged 24–35 months, having siblings,
Acknowledgement
Our survey was funded by UNICEF, and experts from UNICEF gave their precious advice and prompt response to our survey's proposal.
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