ABSTRACT
Background: We aimed to evaluate whether the density of vaccination workers was associated with the immunization coverage in Zhejiang province.
Methods: The immunization coverage of measles-containing vaccine (MCV), the third dose of diphtheria, tetanus, and pertussis combined vaccine (DTP3), and the third dose of poliomyelitis vaccine (PV3) was selected as the dependent variables. Immunization coverage data of children aged 13–23 months were taken from the Zhejiang immunization information system (ZJIIS). The aggregate density of vaccination workers was an independent variable in one set of regressions, while the full-time and part-time vaccination workers were adopted separately in other sets.
Results: The density of total vaccination workers was positively and significantly associated with the immunization coverage (MCV: AOR = 3.36; DTP3: AOR = 2.68; PV3: AOR = 2.37). However, when the effects of full-time vaccination workers and part-time vaccination workers were assessed separately, we only found that the density of full-time vaccination workers was positively and significantly associated with the immunization coverage (MCV: AOR = 5.59; DTP3: AOR = 4.13; PV3: AOR = 3.28). The proportion of migrant children < 7 years and Land area were found as negative and significant factors for immunization coverage.
Conclusions: A higher density of vaccination workers could improve the availability of vaccination services and immunization coverage. We recommended that government or other non-government organization should, apart from vaccine-related assistance, focus their efforts on human resources for vaccination.
Introduction
The vaccine-preventable diseases (VPDs) are among the most common causes of children’s morbidity and mortality. According to the latest estimates from the world health organization (WHO), over 1.4 million children under 5 years of age died from a disease that could have been prevented by a vaccination.Citation1 Of those deaths, measles-containing vaccine (MCV) and diphtheria, tetanus, and pertussis-combined vaccine (DTP) alone could have prevented more than 1 million, which might contribute to reducing 540,000 and 496,000 deaths.Citation2 As we know, the immunization coverage seems to be a key instrument in meeting the goal of reducing under-5 mortality and the immunization coverage of the first dose of MCV is considered as the key indicator for assessing the progress toward this goal.Citation3 Due to the high level of VPD mortality and vaccination being one of the most cost-effective interventions in public health, the Chinese government launched the expanded program on immunization (EPI) since 1978 and continued to invest in efforts to increase the immunization coverage.Citation4
In this study, we focused on the role of vaccination workers in influencing the immunization coverage among children in Zhejiang Province in east China, which could be considered as a research on examining the role of human resource in affecting the public health outcome of infant mortality or under-5 mortality.Citation5–7 Taking it for granted, a higher density of vaccination workers or public health workers may lead to a more optimal immunization coverage if other determinants are equal. Except for implementation of immunization, vaccination workers need to evaluate the eligibility for a specific vaccine, screen the contraindications, prepare the vials for use, and record the vaccination. Besides, vaccination workers also need to monitor the cold chain that keeps the vaccines stored and transported at the appropriate temperature to ensure the efficacy, and they also need to conduct the health education to inform parents and other community members about the benefits and possible risks of vaccination.Citation8,Citation9
In spite of the potential role of vaccination workers, the extent to which human resource for health influence immunization coverage is largely unclear, when other risk factors are sometimes taken into account. A previous study using “regression analysis based on worker density and health outputs around the world” demonstrated that “a density of 1.5 workers per 1000 population was associated with the immunization coverage of 80% for MCV.”Citation10 However, this study did not control for other potential impact factors that could affect the immunization coverage, like household income, maternal education level, etc. As such, the conclusion of the density of vaccination workers associated with 80% coverage might depend on the values of the other risk factors.
On the other hand, there were numerous determinants of the childhood immunization coverage from household-level or individual-level,Citation11–18 but none include vaccination workers as an explanatory variable. For example, only two reports had examined the risk factors of immunization coverage; however, neither included human resources for health as an independent variable.Citation10,Citation13 One study even did not consider health workers as an explanatory variable at all,Citation12 and another mentioned but then excluded “health personnel” from their final regressions model.Citation16 In that study, variables were dropped for reasons like “these variables were not significant” or “the inclusion of variables reduced the sample size to a point where the results did not appear robust to small changes in the data or the specification.” The authors did not make a clear statement on the exclusion of the “health personnel” variable.
Zhejiang is a developed province with a large population of 70 million people located in east China, with an estimated 496,765 births in 2019 and an annual population growth of 0.7%. Since 1978, Zhejiang Province initiated the EPI and has administered over 25 million doses of vaccines each year according to the immunization schedule recommended by the Ministry of Health (MoH) of China. The target of the immunization coverage rate is set at 90% for all the vaccines, which is required to reach herd immunity and interrupt community transmission for all vaccine-preventable disease.
This study aimed to examine the association between the level of childhood immunization coverage and the density of vaccination workers and to find out the potential risk factors that were likely to affect the coverage.
Methods
Choice of dependent variables
The level of immunization coverage of three different vaccines was selected as the dependent variables in this study: MCV, the third dose of DTP(DTP3), the third dose of poliomyelitis vaccine (PV3). More precisely, these dependent variables measured the immunization coverage with valid vaccinations, namely, the proportions of children who got these vaccine doses in the appropriate age window. Based on the recommended vaccination schedule from Chinese MoH, each child needs to get the following vaccine doses before its first birthday: a birth dose of Bacille Calmette-Guérin (BCG), three doses of PV (the first and second dose is injected in activated PV and the third dose is oral PV), three doses of DTP, three doses of hepatitis B vaccine (Hep B), one dose of MCV, and one dose of Japanese encephalitis vaccine (JEV) ().
Table 1. The childhood immunization schedule before 12 months of age in China
The main reason for choosing immunization coverage for MCV and DTP3 as dependent variables were that these two vaccinations were likely to avert the largest number of deaths,Citation19 and they were used to monitor the childhood immunization coverage and its trends. Using the immunization coverage for MCV and DTP3 as the separate dependent variables could allow for the possibility of disparity in the association between the density of vaccination workers and the two vaccination variables. According to the primary immunization schedule, a child needs to get only one dose of MCV by its first birthday while needs to get three doses of DTP in the same age window, which was denoted as DTP3.Citation20 Therefore, for a child to be fully immunized against DTP, the contact between vaccination worker and child needs to occur more frequently than for the child to be immunized against measles. Another difference between these two vaccines is that MCV, unlike DTP, is sometimes delivered in short-term campaigns,Citation21 as well as through routine immunization according to the recommendation of China’s MoH.
We chose immunization coverage for PV3 as a further dependent variable, even if poliomyelitis was responsible for a few deaths. PV, unlike MCV, needed to be administrated for multiple times, the completion of which was denoted as PV3. Moreover, PV was delivered not only by the routine immunization but also by the supplementary immunization activities (SIAs) such as “national/local immunization days”Citation22 As the routine vaccination, PV was administered within the routine vaccination clinics, most of which were set in the community health service centers located at the town level. However, the PV also could be delivered through the SIAs, which needed the house-to-house vaccination service. For these activities, the full range of available human resources from unskilled volunteers to highly skilled workers, whether inside and outside the health sector, were temporarily recruited as ‘vaccination workers’Citation23 Since the coverage of PV3 would be affected by the informal workforce or volunteer, the association between vaccination workers and the immunization coverage of PV3 might differ from that of either DTP3 or MCV.
Choice of independent variables
The independent variables were from four aspects: socioeconomic development level, the land area of the county, the proportion of migrant children (referred to a child whose current residential address was different with the place of household registration) and the vaccination workers. The Gross Domestic Product (GDP) per head of population for each county was included as the potential determinant of the socioeconomic aspect. The hypothesis of including the land area as an independent variable was that we expected a county with a larger land area to have lower immunization coverage in general as vaccination workers would be more thinly spread geographically and the distance between vaccination workers and target children might be greater. According to the previous reportsCitation24–28 on the relation between migrant children and immunization coverage, the proportion of migrant children under 7 years (the number of migrant children aged < 7 years divided by the total number of children aged < 7 years) for each county was considered as an independent variable.
The vaccination workers could be categorized as full-time vaccination workers who took the vaccination as a full-time job and part-time vaccination workers who took the vaccination as a part-time job or act as the unskilled volunteer in the vaccination campaign. Three measures of vaccination workers were used in this study: first, we included the sum of all vaccination workers as an aggregate variable, such as full-time vaccination works and part-time vaccination workers. Second, we evaluated the effect of different types of vaccination worker on immunization coverage. Third, the densities of all vaccination workers, full-time vaccination workers, part-time vaccination workers per 10,000 population at a county level were calculated as the independent variables.
Data sources
The immunization coverage on target vaccine doses was extracted from Zhejiang Immunization Information System (ZJIIS),Citation29 which was an electronic immunization record system established in 2004 and enrolled all vaccination clinics and almost 90% of the children were registered in ZJIIS.Citation30 Every child under 7 years as well as migrant child should be registered in ZJIIS with a unique identification number when he/she visited any vaccination clinic for the first time.Citation29 Children born from 31 August 2018 to 31 August 2019 (aged 12–23 months) registered in ZJIIS were enrolled in our study. Vaccination records of target children were queried from the provincial database of ZJIIS on 1 September 2020.
The immunization coverage was defined as the proportion of children registered in ZJIIS who received the vaccine doses of interest at any time before their first birthday. All vaccine doses including those given in SIA were included in the assessment of coverage. The proportion of might children under 7 years were also calculated by dividing the number of migrant children by the total number of children registered in ZJIIS. Our data on densities of vaccination worker of each county were extracted from the Zhejiang provincial EPI census of 2019, which was reported annually by the 90 centers of disease control and prevention (CDC) at the county level and collated by the Zhejiang provincial CDC. As these data were cross-checked with alternative records like censuses or recent publications, it was considered as the most reliable and latest dataset on vaccination workers currently available. Data on other independent variables such as the total population of each county, GDP per person, and land area (defined as a county’s total area, excluding area under inland water bodies) were obtained from the Zhejiang Provincial Bureau of Statistics of 2019.
Data analysis
Description analysis was used to present the immunization coverage for each of the three vaccine doses, the densities of vaccination workers, and other independent variables for all of the 90 counties in Zhejiang province. The immunization coverage of each vaccination was dichotomized as “<90% or ≥90%.” The relation between immunization coverage and vaccination workers was estimated by using the single-level logistic regression model, and the adjusted odds ratio (AOR) with 95% CI was calculated. Two sets of logistic regression were presented: first, we regressed the level of immunization coverage against the density of the total vaccination workers, while controlling for GDP per head of population, the proportion of migrant children aged under 7 years and land area. The second set of regressions mimicked the first set, but with the density of full-time vaccination workers and part-time vaccination workers as the separate independent variables. All the analyses above applied Stata® 15 (StataCorp LLC, USA).
Results
The mean and standard deviation (SD) and range of all dependent and independent variables of Zhejiang province are presented in . The average immunization coverage at the county level for MCV, DTP3, and PV3 was 97.06%, 94.58%, and 96.25%, respectively. The proportions of counties that the immunization coverage was ≥90% were 96.67% for MCV, 91.11% for DTP3, 93.33% for PV3. Furthermore, the GDP per person, the proportion of migrant children < 7 years and the land area was 98643.06 (CNY), 46.26% and 1131.06 (Km2) per county in average. The densities of total vaccination workers, full-time vaccination workers and part-time vaccination workers were 1.51 (per 10,000 population), 0.09 (per 10,000 population), and 1.42 (per 10,000 population), respectively. The density of total vaccination workers in aggregate terms was positively and significantly associated with the immunization coverage of all three vaccine doses (MCV: AOR = 3.36; DTP3: AOR = 2.68; PV3: AOR = 2.37) after controlling other independent variables.
Table 2. Description analysis of dependent and independent variables
When the densities of full-time vaccination workers and part-time vaccination workers were entered separately in the logistic regression models, the density of full-time vaccination workers was positively and significantly associated with the immunization coverage of all three vaccine doses (MCV: AOR = 5.59; DTP3: AOR = 4.13; PV3: AOR = 3.28) (). However, the density of part-time vaccination workers was not significantly associated with the immunization coverage of all three vaccine doses.
Table 3. Multivariable analysis on assessing the association between vaccination coverage and human resources of public health
The proportion of migrant children < 7 years was found as a negative and significant determinant for all of three vaccine doses when the density of total vaccination workers and the density of full-time vaccination workers were set as independent variable separately. The land area of the county was found as a negative and significant determinant for all of three vaccine doses when the density of full-time vaccination workers was set as an independent variable.
Discussion
The density of vaccination workers was found as a significant factor of immunization coverage, which could be self-evident at the individual level since immunization was administrated in an interaction between a vaccination worker and a person seeking those services. However, this association might be less evident at the population level previously. We assumed the significant association between vaccination workers and immunization coverage at the population level would be due to the reasons as follow: vaccination workers would not spend their all working time in administrating vaccines in China because some of them should undertake other public health service such as the notification and investigation of notifiable communicable diseases or maternal and child health, etc.Citation31 Since the demand for immunization was not concentrated in time or place, vaccination workers need to be available over time and space to meet the continuous and rising demand. Moreover, children need to be administrated in moving windows over time as they were born through the year based on the immunization schedule. Thus, vaccination workers were required to deliver vaccination service uniformly over the year, even if most of their time would be spent in providing other health services.Citation32 Given the precondition of other factors being equal, the higher the density of vaccination workers, the higher would be the availability of immunization services over time and space. Similarly, it was more possible that immunization would take place and a more higher immunization coverage could be observed.
Additionally, the greater availability of immunization services made possible by the higher density of vaccination workers, other pathways contributing to this association at the population level would be existed.Citation33–36 For example, vaccination workers would increase the vaccination demands through educating parents on immunization or raising the general awareness of health in the community. They also could spend their work-time in ensuring the continuous vaccine supply and storing the vaccines properly. Vaccination workers could train the unskilled volunteers to administrate vaccinations in case of the SIAs on PV or MCV, which would also increase the immunization coverage indeed. We suggested that further studies be necessary to investigate the influence of the different pathways between the density of vaccination workers and the improved immunization coverage.
Our results that the density of full-time vaccination workers was a significant factor of immunization coverage, while the density of part-time vaccination workers was not, could be due to the administration of vaccine dose in the most circumstance in developing countries was by full-time vaccination workers, but not part-time vaccination workers.Citation34,Citation35 Obviously, part-time vaccination workers had the ability and were a license to administrate vaccines and ancillary tasks, but they might find other health services they did, which full-time vaccination workers had no time to do, were more pressing, professional or financially rewarding than vaccination. The opportunity cost of part-time vaccination workers’ time could be too high to deliver the immunization service. As a result, part-time vaccination workers would actually give immunization for none or a negligible fraction of their work-time and an increase in the density of part-time vaccination workers would not lead to a significant change in immunization coverage. Inversely, full-time vaccination workers could take advantage of their work-time to educate caregivers, participating in SIAs, and training volunteers, which could be valuable and meaningful to increase immunization coverage.
In addition to the results that the density of full-time vaccination workers was significant in accounting for the immunization coverage of all three vaccine doses, it was interesting to note that its coefficient was similar in size across them. The robustness was found despite difference among vaccines in the number of doses required for full immunization, in models of administration (oral versus injected), and in the use of SIAs. Whatever the accurate role of full-time vaccination workers in the three different regimens (e.g., practicing routine immunization, training or supervising unskilled volunteers), it indicated that the full-time vaccination worker was a sufficient and prerequisite human resource to achieve an optimistic coverage.
In this study, the migrant children under 7 years were found as a negative determinant for the immunization coverage of all three vaccine doses in both two regression models with the density of total vaccination workers and the full-time vaccination workers as an independent variable. Our finding probably demonstrated that the awareness of and the accessibility to vaccination service were different between migrant parents and resident parents.Citation37 As migrant people might spend more time and effort to adapt to the new sociocultural environment and suffer a poor living condition, they were unlikely to consider childhood vaccination as a higher priority in their daily life.Citation38 Another interesting finding was that migrant children under 7 years were more significant and had larger AORs for DTP3 and PV3 than for MCV. It could be assumed that MCV needed only one dose, whereas DTP3 and PV3 needed three doses with an interval of one month according to the immunization schedule. A one-time visit to a vaccination clinic might be motivated by purposes other than vaccination, but subsequent visits at predetermined times required the advance planning, for which the education level of parents would be helpful. Although the PV, as well as DTP, needs to be administered multiple times for a child to be fully immunized, poliomyelitis, unlike diphtheria, tetanus, and pertussis, had focused on a global eradication objective. These activities were likely to diminish the importance of literacy and health awareness of migrant parents in impacting the immunization coverage. We recommended that interventions such as outreach or adjustment of session time be conducted to improve the immunization coverage among migrant children.
In the regression model with the density of full-time vaccination workers, the land area of each county was negatively determinant for the immunization coverage of all three vaccine doses. Given the fixed number of full-time vaccination workers, the density would be spread more thinly over space where the land area was much larger. It meant that the geographical availability of vaccination services be smaller. A decrease in spatial availability added to the barriers, including time and travel costs, of getting the vaccination, or vice versa.Citation39
The GDP per person was not found as a significant risk factors for the immunization coverage of all three vaccine doses whether aggregate the vaccination workers or not. It was reported that the social-economic development was significant in decreasing the maternal, infant, and under-5 mortality, but it obviously did not impact the immunization coverage. Moreover, other factors that would be influent by the social-economic development status could be associated with the mortality rate but were unlikely to impact immunization coverage.Citation40,Citation41 For example, nutrition, safe water, and sanitation. In China, the budget for vaccine procurement was covered and allocated at the central level, but the budget for vaccination practice, cold chain maintenance, vaccination worker’s training, surveillance, and community health education was covered and allocated at the peripheral level. GDP did cover some aspects that should be expected to affect the immunization coverage, but those were only a small fraction of GDP. Furthermore, this fraction varied across areas but cross-area variations in GDP per person would not reflect an actual difference in expenditure on the vaccination program, which was still a coarse measure of vaccination-related expenditure. In this study, the association between GDP per person and immunization coverage was evaluated only in a province due to the data limitation. This association would be significant in other areas or in the whole of China, which could be tested in future studies.
This study is subjected to two limitations. First, only children with vaccination record in ZJIIS were included in the analysis. It could overestimate the immunization coverage and impact the association between the immunization coverage and the density of vaccination workers as these children were more likely to be vaccinated and migrant child new to the area might not be registered in ZJIIS in a timely manner. Second, the independent variables other than the density of vaccination workers were limited due to the data limitation, which would be addressed in a special survey in the future.
Conclusions
The results of our study implicated the importance of vaccination workers for immunization coverage among children at the county level in Zhejiang Province. It also provided an indirect evidence for the WHO assertion that human resources may be “a ‘major barrier’ to improving immunization coverage.” A significantly higher immunization coverage would be observed if we increased the density of vaccination workers. Furthermore, larger increases should be needed in areas with a larger land area or with a higher proportion of migrant children. We recommended that government or other nongovernment organization that interested in EPI should, apart from vaccine-related assistance, focus their efforts on human resources for vaccination.
Author contributions
Y.H. and HK.L. conceived and designed the experiments; H.L. and Y.C. performed the experiments; Y.H. and Y.W. analyzed the data; Y.W. contributed reagents/materials/analysis tools; Y.H. wrote the paper.
Disclosure of potential conflicts of interest
The authors declare that they have no competing interests.
Ethics approval and consent to participate
This study was approved by the ethical review board of the Zhejiang provincial CDC. Written informed consent was obtained from a legal caregiver of each eligible child and health workers enrolled in this study.
Acknowledgments
We appreciate the critical review of the manuscript by Yiming Zhu, School of Public Health of Zhejiang University, Hangzhou, China.
Additional information
Funding
References
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