Ethics statement

Ethical approval was obtained from the Kebbi State Health Research Ethics Committee, KSHREC, (under the Kebbi State Ministry of Health) with a registration number KSHREC: 106: 20/2021 in a letter dated 4^th May 2021. Clearance was also obtained from the school of global health and bioethics through the faculty coordinator, Euclid University, before proceeding for the field investigation. The investigator obtained a formal verbal consent from the study participants.

Study area

Kebbi State is a northwestern States of Nigeria with local and international borders. Locally, it borders Niger, Sokoto, and Zamfara States, while internationally, it borders Benin and Niger Republics [24]. Kebbi State enjoys a tropical climate characterised by annual rainfall ranging from 800 mm (northern part of the State) and 1000 mm (in the south), while temperature ranges from 21 to 40 degree Celsius [8]. However, climate change seems to have begun to impact, as seen in temperature excursions beyond 40 degrees Celsius (as much as 43 degrees) in recent times. There are 21 Local Government Areas (LGAs), 225 political wards and four traditional Emirates in the State [8]. It has a projected population of 5,119,659 (2021) and an under-one population of 204,786.

Basic structure of AEFI surveillance system in Nigeria

At the health facility, the routine immunisation (RI) provider line-lists all the AEFI cases. In the event of a serious AEFI, the RI provider completes the line-list and AEFI reporting forms and transmits them to the LGA Disease Surveillance and Notification Officer (DSNO) and LGA Immunisation Officer or Routine Immunisation Officer (LIO/RIO) within 24 hours, using mobile phone or SMS or WhatsApp or any other telecommunication medium. The alert should also be sent to NAFDAC via SMS and it should trigger the use of an investigation form by the State Investigation Team. On the other hand, the monthly line-list of all AEFI cases is submitted to LGA DSNO. The summary record is also submitted to the LGA Monitoring & Evaluation (M & E) officer for data entry in the District Health Information System 2 (DHIS2) platform. If there is no detected case for the month, zero reporting can be done using the appropriate AEFI surveillance form.

There are two AEFI information/data management channels in place- Integrated Disease Surveillance and Response (IDSR) and District Health Information System 2 (DHIS2). The LGA DSNO captures the monthly summary of the AEFI report onto IDSR 003 and submits the line list to State DSNO while the LGA M & E officer captures the summary into the DHIS2 platform, which can be assessed by the individuals granted access at Zonal and National levels. The State DSNO captures the AEFI data into the AEFI database for proper archiving and analysis for decision-making. The State DSNO also transmits the AEFI data to the National level.

For those private medical institutions conducting immunisation services and treating AEFI cases, all AEFI reports are sent to their respective LIO/RIO within the institution or facility’s catchment area, who will then share them immediately with the LGA DSNO. In the context of an immunisation campaign, vaccinators are to submit the report immediately to team supervisors. The supervisors assess the validity of data without delay. The supervisors relay or submit the report to the Ward Focal Person, who is expected to report to the LIO, who in turn shares it immediately with the DSNO. Parents, caregivers, vaccinators, or healthcare workers within the communities can also notify the health facility about the AEFI cases, especially in a mass vaccination campaign setting, and this can be documented at the health facility for proper management.

Study population

The study population includes the Routine Immunisation Service Providers at HF level, Routine Immunisation Officer, Local Immunisation Officers, Disease Surveillance and Notification Officers and Monitoring and Evaluation Office at the LGA level. At the State level, this included the State Director of Immunisation, and State Epidemiologist. State Partners were also interviewed, including WHO officers- Surveillance Focal Person, Routine Immunisation Officer, Data Assistant, and UNICEF’s Communication for Development Officer. National Officers were also included in this study to enrich the findings and provide broad and upstream (national level) perspective on the AEFI surveillance system in Nigeria. Though not exhaustive, these are the key officers whose responsibilities have a strong bearing on immunisation service delivery, AEFI monitoring, reporting, and documentation and communication strategies. The study population is competent, qualified, and well-positioned to provide original and correct information regarding the barriers or challenges confronting optimal vaccine pharmacovigilance (safety monitoring) in Nigeria.

Study design

A qualitative research design (using a ground theory approach) was adopted using in-depth interviews with key informants and focus group discussion. We conducted ten key informant interviews (IDIs) and two sessions of Focus Group Discussions (FGDs) among the study population to elicit information on the barriers impeding optimal AEFI surveillance and documentation in Nigeria.

Sampling technique and data collection

Focus Group Discussions (FGDs) were conducted among the LGA-level Managers of the selected LGA Primary Health Care Department by the Principal Investigator (SAO). The selected health managers have job function with a bearing on immunisation service delivery, including AEFI surveillance. Conducting FGD sessions provided an in-depth understanding on the subject of investigation. We selected the three LGA-level Managers from each of the three distinct categories (by job functions) from the 21 LGAs. The selection of the three individuals from each category for the FGD was guided by performance based on the routine (secondary data) completeness data for AEFI by LGA in Kebbi State. Specifically, three officers from each distinct category (by job function) from three good performing LGAs and ditto for the poor performing LGAs. The selected LGAs by classification were Augie, Koko-Besse and Sakaba (good performing) and Aliero, Yauri and Zuru (poor performing) respectively. Consequently, a total of 18 officers from the three groups were selected for the FGD at the LGA level. The FGD was conducted in two sessions (a total of 18 participants, i.e., nine participants in each session).

The Principal Investigator (SAO) also conducted in-depth interviews of the key informants for senior officers at the State and National Levels. KIIs were conducted with the State Director of Immunisation, State Director of Public Health, and State Pharmacovigilance Desk Officer from NAFDAC, to provide an in-depth understanding of the phenomenon of interest, i.e., AEFI surveillance and documentation barriers and bottlenecks. At the federal level (national), the IDIs at the State level were complemented massively by interviews with senior officers- Directors from the pharmacovigilance and surveillance focal points at National Agency for Food and Drug Administration and Control (NAFDAC)and National Primary Health Care Development Agency (NPHCDA) respectively. Health Development Partners at the State level, such as the WHO officers- RI and Surveillance Focal Points, and Data Support Officer and Communication for Development Officer for UNICEF were also interviewed.

Overall, a total of 10 IDIs and 2 FGD sessions (involving 18 participants in the two sessions) were conducted for this study. There was no case of refusal to participate in this study. The IDIs and FGD sessions were either virtual or physical, depending on the convenience and availability of digital technology on both sides (interviewer and the study participants). Most of the interviews were conducted face-to-face with the study participants. These interviews were either held in the office or at end of a joint programme review meeting involving LGA Level Managers. The interviews were recorded in audio and stored in an archive. A few (two) virtual interviews (for the key informants) were conducted with national level officers from the NPHCDA and NAFDAC. The qualitative interview for each FGD session lasted for a maximum of an hour, while the IDI lasted for a maximum of 50minutes. The participants were provided with their interview transcriptions for validation before data analysis. Ultimately, the decision to discontinue recruitment into the study was guided by data saturation when no new information was generated from the participants’ interviews.

Interview guide

Though the participants were given ample opportunities to freely express their views and opinions about the subject of interest, an interview guide serves as an aid for the interviewer (principal investigator) to elicit answers to the research questions. The interview guide was constructed from the research objectives and the existing literature on the subject of investigation.

Data analysis

The researchers cleaned the data, processed and analyzed the data manually for the qualitative survey using a thematic framework approach. The process involved verbatim transcriptions of returned audios from professional transcribers who were not part of the investigation. The transcripts were screened, edited, and double-checked independently by the research team for accuracy, consistency, and clarity. The note taken during the interview sessions were used to guide the screening and editing to improve the overall quality of the transcription (transcribed data). Further analyses involved sorting, coding, and thematic identification. The coding was developed based on the objectives of the study, the research tools, and the responses elicited from the study participants.

We generated themes and sub-themes that were consistent and relevant which provided a framework for a better understanding of the research topics and objectives. Subsequently, we used the content analysis method to generate qualitative data. Content analysis compresses texts into replicable, fewer content categories based on clear coding rules [25]. Therefore, I (SAO) summarised responses to each theme and sub-theme and ensured that relevant and important expressions like quotations by the respondents were reported verbatim to enrich the outputs of the study.

Trustworthiness of the qualitative study

This qualitative research study is trustworthy based on these criteria: credibility, transferability, dependability and confirmability.

Research team

Regarding the research team, the principal investigator (SAO) managed the sessions effectively, given that the researcher was orientated in the past and had moderated a few FGD sessions for the WHO Academy in late 2020. He has also published two studies using the qualitative research approach. The other authors (MB and LCK) have either had training or had published qualitative studies. In addition, SAO (male) is a medical doctor, works within the disease surveillance and immunisation sphere with the World Health Organization and a doctoral student at the time of the research. He has extensively worked in the study setting and developed excellent professional relationships with the key stakeholders, especially at the primary health care level. LCK (male) is a senior author, had a doctoral degree, had investigated and published on vaccine hesitancy using a qualitative approach. He is the Faculty Coordinator at the School of Global Health and Bioethics, Euclid University. The third author (male), MB had a doctoral degree in Biostatistics and Statistical Science and works with the Euclid University.

Theme: Bottlenecks and challenges confronting AEFI surveillance system

Impediments to optimal AEFI surveillance and documentation in Nigeria

Regarding the bottlenecks and challenges confronting optimal routine AEFI monitoring, reporting and documentation in Nigeria, the respondents working at the health facilities provided important details, such as the work overload (arising from human resource deficit), lack of knowledge about the value or relevance of the reporting and documenting AEFI cases (serious and non-serious) and sub-optimal understanding of the reporting format and cumbersome documentation process. Similarly, evidence from higher-level stakeholders’ interviews showed poor knowledge of what needs to be reported.

In a study conducted in Alimosho LGA, Ogunyemi and colleagues reported not knowing about the notification and reporting system and process, inability to find forms, and not considering the event as related to immunisation are some of the barriers to optimal AEFI reporting [21]. In the same vein, a study conducted at Sabon Gari LGA, Zaria, in the northern part of Nigeria, reported not considering the event related to immunisation, ignorance of the reporting processes, and time constraints, perhaps due to competing demands or excessive workload [20]. Similar to this study’s finding, Yamoah et al. reported from a study among health care professionals in Ghana that cumbersome bureaucratic process of reporting, complex data collection tools and busy work schedule (work overload) were impediments to reporting and documentation of AEFI [26]. Another study from Ghana, published in 2020, highlighted multiple barriers to reporting which were largely similar to this and previous studies [27]. The identified barriers were lack of knowledge or training and not believing an AEFI was serious enough to be reported [27]. Unlike many previous studies, including this study, reporting forms were readily available at the health facilities at the time of interviews in most health facilities [27].

A study from Zimbabwe that analysed spontaneous reporting, Vigibase, from 1997 to 2007 also documented competing work priorities, insufficient reporting resources and inadequate knowledge deficit due to insufficient training of health workers [28]. Similarly, Malande et al. reported from Kenya that excessive paperwork and effort and the non-availability of reporting tools for documentation were impediments to AEFI reporting and documentation [29]. A study from Gaza in the Middle East identified some impediments to AEFI reporting and documentation, such as high workload, not considering AEFI related to immunisation and absence of guidelines, protocols and notification forms [30]. Similarly, a study from the Far East, India, among Pediatricians in Kerala reported, among others, difficulties in reporting processes (paper-based reporting forms) and time constraints and work pressure, less formal training (comparatively lower knowledge of reporting and reporting processes) among private health care providers as barriers to AEFI reporting [31].

Findings from studies from developed countries such as Australia, Canada, United States of America buttressed findings from this work and other published work conducted in developing countries. For example, studies conducted in Australia, the United States of America (USA), the United Kingdom, and Canada indicated that unclear definition of reportable AEFI, not knowing AEFI reporting was expected or events deemed not serious enough to be reported were barriers to AEFI reporting and documentation [32–34]. Like other studies from some developing countries cited above, two studies from the USA also reported that health care professionals mentioned a lack of awareness of the reporting procedure or confusion as to who is responsible and when to report as barriers to optimal AEFI reporting and documentation [32, 34, 35]. Lastly, time constraint/pressure to complete the reporting forms was identified as a barrier by studies conducted in Australia and the United Kingdom [33, 34].

A global review of records and immunisation safety monitoring data between 2010 and 2019 found gaps in global immunisation safety monitoring, especially in Africa, Western Pacific, European and Eastern Mediterranean regions [17]. The report also identified a lack of reporting tools and poor health workers’ understanding of AEFI [17].

This study also found an attitudinal problem of the health workers as a significant impediment as commitment is lacking in many cases. A study conducted at Sabon Gari LGA, Kaduna State, northwestern Nigeria, among primary health care workers identified two attitudinal elements- forgetfulness and lack of interest- as barriers to AEFI reporting [20]. As reported by the health workers, forgetfulness may be related to excessive workload and non-prioritisation of AEFI reporting and documentation as an integral part of immunisation programme. The apathy could be explained by a poor understanding of the benefit and integral nature of AEFI in immunisation programmes. It could also stem from demotivation and poor working conditions of health workers in the study setting. Internationally, Mehmeti et al. reported the lack of interest as a barrier to reporting AEFI in Albania [36].

Fear of reprimand, i.e., feeling that the cause of the AEFI is a result of inadequacies in their professional practices, remains an important impediment to optimal reporting and documentation of AEFI cases at the PHC level. Several published papers from within and outside Nigeria have identified fear of reprimand, fear of personal consequences/punishment, fear of being victimised, or fear of raising public alarm as part of the major barriers to reporting and documentation of AEFI [17, 27, 37–41]. Unlike a few other studies, this piece of work did not find that the fear of litigation or adverse events was not reported because of inherent trust that licensed vaccines are safe [32, 42, 43]. The preponderance of the fear of reprimand or punishment and fear of victimisation or personal consequences as a barrier to detection, reporting and documentation of AEFI (frequent findings in LMICs) are all a reflection of poor or lack of training on AEFI (pre- and in-service training), weak supportive supervision, non-prioritisation of AEFI and weak governance. As mentioned above, the poor situation requires urgent attention by stakeholders at all levels to address the background causes or triggers of the identified factor/barrier. Therefore, this work adds to the growing international call for introducing courses on AEFI -causes, management, surveillance and reporting, to medical and nursing educational curricula. Previously published works have also confirmed this increasing need, as observed in Canada, the USA, Europe and Australia [32, 33, 44–46]. Beyond the pre-service training in higher health institutions (medical and nursing schools and college of health technology for community health workers), there should be periodic statutory in-service training for immunisation service providers and surveillance officers. These, among other measures, will reverse the current sub-optimal performance of AEFI surveillance and documentation in LMICs (including Nigeria) and beyond.

Concerning the role of the caregiver’s educational level and adherence to immunisation services, the higher the level of educational status of the mothers/caregivers, the more likelihood of adherence to the immunisation schedule [47] By extension, this role of mothers’ educational status could impact the likelihood of detection and reporting of AEFI by caregivers. In our study setting, the educational status of women is lower than men, where the majority live in the rural environments. These and other socio-ecological elements interacting together might have negatively influenced their capacity to use the limited health information provided by the health workers. This could explain the low level of awareness and sub-optimal AEFI reporting by parents/caregivers in this study.

The government’s non-prioritisation of AEFI surveillance and documentation as a core component of routine immunisation service delivery was identified as an impediment to optimal AEFI surveillance and documentation in this study. This also translated into the lack of funding, weak stewardship and governance of pharmacovigilance in Nigeria. It has also manifested in the sub-optimal coordination between the national regulatory agency and immunisation programme (EPI) implementing agency, as seen in the slow pace of efforts towards implementing electronic AEFI surveillance, specifically the Med Safety App, being promoted by NAFDAC- the national regulatory agency. Weak coordination and stewardship are commonly reported in LMICs [17, 48]. Further, this study indicated that partner agencies, such as WHO, have been the vanguard of strengthening the AEFI surveillance system in Nigeria. Few reports and reviews have identified weak political will and coordination by governments in LMICs as part of the barriers to a strong vaccine safety monitoring system, i.e., AEFI surveillance and documentation [38, 49].

A sequela to the above factor is the non-availability of a dedicated budget line or funding stream to support routine AEFI surveillance and documentation activities (except during campaigns- SIA or OBR). During SIA or outbreak response, partners agencies, donors and government often pool resources together to train health workers, provide logistics and set up a vaccine safety monitoring system during the campaign implementation. This study also found that State and LGA AEFI committees are moribund (outside the campaign and OBR modes) due to the non-availability of logistics to hold regular meetings and undertake monitoring and investigation of serious AEFI cases. Evidence from global studies and expert reviews indicated little or no funding dedicated to supporting vaccine safety surveillance and pharmacovigilance in LMICs, especially in Africa [17, 49–51]. Thus, corroborating this study’s finding.

The funding and logistics challenges limit supportive supervision of AEFI surveillance activities, especially in rural areas. This was clearly pointed out by critical stakeholders that were interviewed in this study. Supportive supervision could be defined as a range of measures to ensure that personnel carry out their activities effectively through direct, regular personal contact to guide, support and assist designated staff to improve their work competency [52]. It is one of the operational components of the “Reaching Every District” strategy, aimed at improving immunisation performance in every district (including health facilities), especially in the African region, where access and utilisation of immunisation services are suboptimal [53]. Supportive supervision has improved equity and immunisation service delivery efficiency [52]. A study conducted by Gbenewei et al. reported that the deployment of supervisors during the campaign (mass immunisation programme) might play an important role in improving the identification and reporting of suspected AEFI [54]. Further, a randomised control trial in Cameroon to assess the effect of sending weekly SMS and weekly supervisory visits on AEFI reporting rate during a meningitis immunisation campaign conducted in Cameroun using Meningitis A Conjugate vaccine, found supervision more effective than SMS or routine surveillance in reporting AEFI [55].

However, a pointer to the complementary roles of adequate funding and logistics in improving and achieving quality immunisation services (AEFI surveillance and documentation inclusive) has been established in the literature, corroborating this study’s funding. For example, ‘a quasi-experimental study’ conducted in India, a lower-middle-income country, to assess the effect of supportive supervision on immunisation session practices indicated that there is a need to address systemic issues, such as essential logistics and supply chain management and financial resources that could complement the supportive supervision strategy to improve immunisation service delivery [56]. Similarly, a review of immunisation programmes conducted across 20 East and Southern African countries from 2012 to 2018 found that half of the countries examined had inadequate operational funding, evidence of cancellation of outreach services and supportive supervisory visits due to lack of funding or operational funding, while nine countries had weak vaccine stock management system characterised by stock-out of vaccines and supplies [57]. Indeed, the findings in this study have been strongly buttressed by reports across similar settings in LMICs, indicating the identified challenges of human resource deficits, inadequate logistics and vaccine management system, lack or inadequate operational funding for transport and fuel for cold chain equipment, among others [58, 59]. From the above, there is a need to invest in the operational readiness (fueling, operational cost e.t.c), vaccine management and supply chain system, and of course, specific attention should be paid to AEFI supportive supervision being aided by the aforementioned functional systems in place.

The study also found a lack of prepositioned AEFI kits to manage serious and non-serious AEFI cases at health facilities as one of the challenges of achieving a functional and responsive AEFI surveillance system. Only a report from India mentioned a similar challenge with the availability of AEFI kits at the HFs, where vaccination services were provided [60]. There was no dedicated transportation facility or mechanism to facilitate referral mechanisms for serious AEFI cases in the study environment. The national policy stipulates that treatment of AEFI is free, but this is not the case in practice, as caregivers buy drugs out-of-pocket to treat such adverse event/reaction(s). Similarly, there was no ancillary support, such as psychosocial support services, to address the mental and psychological impacts of the adverse events/reactions.

Further, a lack of feedback and/or non-recognition of their contributions was a disincentive to reporting AEFI at the health facility level. A published study from western Europe indicated non-existent or inappropriate feedback [61], identical to the finding in this study. Similarly, the study from Albania, Eastern Europe, indicated that most of the health workers never got feedback- a lack of communication from the vaccine safety stakeholders [36]. Masuka et al. acknowledged the importance of appropriate and timely feedback to reporters of AEFI to increase the number and quality of AEFI reports [28]. Even in developed countries like Canada, a study among family physicians indicated that they reported uncertainty about causality between the vaccine and the event [32], suggesting a lack of feedback and possibly an information or knowledge deficit. The study also reported the need to give physicians feedback and avail them of learning opportunities on vaccine-associated event reporting [32].

The timeliness and quality of feedback on reported AEFI determine its usefulness to the regulators, vaccine manufacturers, reporters, and the vaccinees or the parents of the vaccinees and the public [61]. A lack of or inappropriate feedback to health workers and parents or vaccinee is a considerable disincentive to further or future reporting as interests tend to wane [51, 62, 63]. Ultimately, confidence in the immunisation programme gets eroded.

Another emerging threat to AEFI surveillance activities at the PHC level is the growing insecurity in northwestern Nigeria. This impacts the frequency of supportive supervision, data transmission, investigation of reported serious AEFI cases and disruption of health services. No investigator has previously reported the role of insecurity or conflict on this subject. Insecurity impacts access and quality of health service delivery. Three relevant pathways were identified based on a study from the Democratic Republic of Congo (DRC), namely violence, mobility restriction and resource availability [64]. The pathways manifest in the availability and quality of the health workforce, access to medicine, health commodities and medical technology, health workers’ and client access to health facilities or restriction of field investigation, transport and analyses of biological samples, etc. All these elements impact the capacity of the conventional health system, including surveillance, to rapidly detect, report and investigation AEFI cases. Therefore, adaptive strategies are highly warranted in the context of insecurity, as seen in Nigeria and countries like DRC and Somalia, to mitigate the disruption of health services, including the surveillance systems.

Some relevant measures or strategies could be employed to ensure AEFI surveillance is uninterrupted in the context of insecurity. Such strategies could emanate from the lesson learned as the polio program evolved in Northeastern Nigeria, where Boko Haram Insurgency turned the region into the last WPV sanctuary in Nigeria and Africa. Similarly, armed banditry, sporadic violence and kidnapping have escalated in the northwestern region- this study’s setting, and sometimes health workers are the victims [65]. Some of the strategies implemented in security-compromised setting were deployment of community informants to detect and notify AFP cases from inaccessible or partially accessible areas, the use of mobile phone applications for Auto-visual AFP Detection and Reporting (AVADAR) by health workers and informants in challenging terrains and insecure areas, civilian-military security partnership and health service delivery among others [66–69]. These strategies can be applied to sustain or build resilience at the PHC level for AEFI surveillance and documentation. The Med Safety App on the android phone being piloted to promote self-reporting of AEFI is akin to the AVADAR innovation that has proven effective in complementing conventional AFP surveillance, particularly in security and geographically challenged locations.

This study’s finding also indicated inadequate communication between the RI providers and the clients (caregivers/mothers). Adequate health education services are not often provided before vaccine administration, such that caregivers/mothers will be able to make well-informed decisions regarding AEFI detection, reporting and follow-up actions. The paucity of information provided by health workers, especially in a setting where female education remains low, could contribute to high drop-out and the high number of partially immunised. This may be largely due to a poor understanding of AEFI and the benefits of full immunisation for eligible children. Oku et al. pointed out that the quality of information provided to caregivers in rural health facilities in Bauchi State, Northeastern Nigeria, focused on polio and were not detailed, perhaps due to a shortage of health personnel [70]. In the Guruve district of Zimbabwe, Constantine and colleagues found that caregivers were not reporting AEFI to the health facilities because they were not educated enough to know that they have to report the events [37]. These findings buttressed our observation on the communication gap between RI service providers and parents/caregivers, impacting immunisation service delivery, including AEFI surveillance and documentation.

Poor community awareness and sub-optimal community linkage were clearly identified as one of the weaknesses of Nigeria’s current AEFI surveillance system. The awareness level and understanding of the need to report AEFI is low in this environment. Inherently, the EPI in Nigeria remains challenged by sub-optimal awareness and understanding of the importance of routine immunisation or vaccination services (SIA/OBR inclusive). Studies have shown that a low level of awareness and weak community linkage impedes the optimal uptake of routine immunisation services and other PHC services [71–75]. In the same vein, low awareness, poor community linkage, and engagement contribute to weak pharmacovigilance, especially low reporting, poor documentation, and limited vaccine and drug safety information [17, 49, 51]. Hence, there should be a systematic engagement of community informants supported with the necessary tool to intensify AEFI detection and reporting from the community level. Media publicity and strengthening existing community resources, such as traditional and religious institutions that had proven useful in other public health programs (Polio Eradication Initiative, Guinea worm elimination etc), should be strongly considered. These best practices have been well documented in Nigeria’s Polio Programme and can be leveraged to improve the sensitivity of AEFI surveillance in Nigeria.

Limitations of the study

The lack of data from respondents working at private health facilities and general hospitals is a limitation of this study. However, the contribution of private health service providers and secondary health care facilities to routine immunisation (RI) services is very limited in this study setting. Indeed, in most of the General Hospitals providing routine immunisation services in the State, the health workers are often seconded by the Local Government Health Authority (PHC level) to support RI services due to human resource deficit. Therefore, the experience is likely to be the same, and the absence of perspectives from these sources is unlikely to change the study findings. Moreover, the proportion of the General Hospitals in the State is less than 5% of the total number of RI service delivery points.

Secondly, the study is limited to one State in northwestern Nigeria. However, the State has 21 LGAs with a population of about 5 million people inhabiting the geographical space. The study could have been extended to other States, but for funding constraints and limited data collection time across a vast country like Nigeria. On the other hand, the finding of this study may largely be similar to what is obtainable in other States and regions of the country. Further, the limitation was mitigated in this study, given the interviews with or perspectives from national stakeholders in Nigeria’s pharmacovigilance system.