Discussion
This is the first known implementation science study in Uganda on determining the effectiveness of using CHWs to obtain quality and reliable data that can be used for planning and evidence-based response actions. Our findings show that CHWs can be successfully employed to obtain target population data, track, and link defaulters to points of immunization services. The findings further show that holding regular monthly health facility immunization data audit meetings, tracking, and linking of defaulters to immunization services are effective in improving immunization coverage. In addition, equity issues were addressed as neglected children who tend to live in hard-to-reach areas such as forest reserves were reached through house-to-house registration and defaulter tracking through home visits.This study found that the collected house-to-house population size was higher than the district estimates by 8.4% representing moderate variance which suggests that district projections based on UBOS census estimates are fairly accurate. Therefore, employing CHWs to conduct house-to-house registration may not be cost-effective on a large scale. However, house-to-house registration for eligible population can be used in hard-to-reach areas with consistent low immunization coverage since such areas tend to have existent health inequities. Given the moderate variance, it is also arguable that using the district projections based on the previous population census in Uganda conducted in 2014 [In this study, the CHWs were given refresher training in EPI service delivery; data management (including review of EPI performance); vaccine management; advocacy, communication, and mobilization. The training lasted for five days, one month before implementation of the study interventions. The CHWs tasks included attending the data audit meetings and conducting home visits to trace and link defaulting children. They were supervised by the health workers involved in EPI service delivery at their respective health facilities to which they were attached. The tasks of the health workers included organizing the data audit meetings; identifying children defaulting at their immunization schedules; reconciling the defaulters who had returned for immunization; and supervising the CHWs.Data monitoring and use through regular meetings coupled with follow up of these partially immunized children through home visits was key to improving coverage in our study. Results showed that the review meetings provided an opportunity for health workers to analyze, appreciate and use EPI data to make programmatic improvements. These audit meetings just like evidence from another study presented an excellent platform for sharing best practices, lessons learned, dialoguing and providing feedback on results of EPI indicators with health workers involved in immunization service delivery [This study showed that using CHWs to track and link defaulters to points of immunization services was a feasible intervention. In our study, overall, more than two thirds (68%) of defaulters returned for catch up immunization. Evidence from a study conducted in Kenya showed that households visited by CHWs were 1.7 times more likely to have fully immunized children than those that were not [There were several reported challenges experienced by CHWs while conducting home visits including lack of protective wear, trekking long distances and lack of financial incentives or remuneration, among others. Similar findings have been reported in studies conducted in Ethiopia [Results from our study further elicited various reasons for children defaulting from their immunization schedules. These included religious beliefs prohibiting uptake of vaccination services; restricted movements due to the COVID-19 pandemic; migration of families for economic activities such as farming; fear of multiple injections; domestic violence, and ignorance of the caregivers on the benefits of immunizations. Similar reasons for defaulting have been reported from studies conducted in; Uganda [We observed significant differences in the immunization coverage between the health facilities in the intervention and control arms for specific antigens at endline. These observed differences may be attributed to the monthly health facility immunization data audits with the identification and followup of defaulters through home visits. A number of studies support our results and demonstrate that defaulter tracking of children through home visits increases immunization coverage [Overall, at endline, coverage for all antigens (except MR in the intervention arm and BCG in the control arm) increased in both the intervention and control arms. The increase of coverage in the control arm could be explained by the fact that during the same period of implementing of activities in the intervention health facilities, there were post-covid-19 pandemic immunization revitalization activities initiated by the district health office and geared to poorly performing health facilities in Mayuge district of which health facilities in the control arm were a part of. In addition, the significant decline in BCG coverage (CHWs can play an important role in attaining universal health coverage by strengthening health systems to provide people centered care that is equitable and culturally appropriate [The cost of implementing the intervention package in the three health facilities over a period of three months was $14,900 including the audit meetings and defaulter tracing that cost $1,230 and $2,560 respectively.This Implementation study had some limitations that need to be acknowledged. There were limitations in obtaining an accurate target population given the possibility that not all under-one-year children (eligible population) were registered during the house-to-house visits. There were five vaccine hesitant households that refused registration and seven households that were found locked as their inhabitants had temporarily migrated to other areas for agricultural purposes such as planting of maize, Therefore, it can be argued that the inaccessible households could have contributed to a higher registered population of under-one-year children during the house-to-house exercise. Another possible limitation could have been contamination between the control and intervention facilities arising from CHWs from the different arms sharing information on the study proceedings in their respective communities. Lastly, the time (three months) for the study implementation was short to observe the meaningful impact of the interventions on the trends of immunization coverage.