Public Health Emergencies (PHEs) are recognized as a major threat to global public health security (1). Many countries experience different types of PHEs including infectious disease outbreaks, natural disasters¹ (e.g., floods), and human-induced hazards (e.g., armed conflicts) (2). In the WHO Africa region, more than 100 PHEs are reported annually (3). A PHE is described as a situation that threatens the health, safety, and well-being of a large number of people and which often necessitates substantial multi-sectoral assistance (2, 4). For instance, the recent unprecedented occurrence of the Coronavirus Disease (COVID-19) pandemic, which is classified as a PHE of international concern (5), has highlighted more than ever that PHEs do transcend international boundaries and have negative impacts on various facets of society including public health (2, 3). The impact PHEs have on public health cannot be understated, given they cause widespread disruption to both the broader health system and provision of health services (6–8) including immunization (9, 10).

The disruption to national immunization programs (NIPs) experienced in countries with PHEs has been associated with suboptimal immunization coverage rates (6, 11, 12). The plummeting coverage witnessed during PHEs is facilitated by reduced access to immunization services, destroyed and disrupted vaccine logistic systems, depleted and diverted financial and human resources for immunization, and reduced trust toward immunization (6, 11, 12). Many of these factors have eminently featured during the COVID-19 pandemic (13–15). The sub-optimal immunization coverage rates, also, create large pockets of unimmunized and under-immunized children and adults thereby lowering herd immunity (16, 17). The compromised herd immunity acts together with other PHE co-existing factors like poor sanitation and overcrowding to provide ideal conditions for outbreaks of Vaccine-Preventable Diseases (VPDs) (18–20). Due to such frailties, countries affected by PHEs are reported to lag in meeting global and regional immunization targets aimed at control, elimination, and eradication of VPDs (21, 22).

The Global Vaccine Action Plan (GVAP) was developed in 2011 to actualize the vision of the Decade of Vaccines (DoV) for having a world where individuals and communities will be able to enjoy lives free from VPDs by 2020 (23). The Regional Strategic Plan for Immunization (RSPI) is a WHO Africa region contextualized immunization framework adopted from the GVAP with goals for attainment by 2020 (24). Although through the two immunization frameworks the WHO Africa region has achieved substantive gain in immunization e.g., the successful eradication of wild poliovirus disease (25), many targets remain unmet, owing to among other factors the prevalence of PHEs (26). During the DoV there has been growing concern on the possible role PHEs play in delaying achievement for set immunization targets (22, 26). According to reports by the WHO, Strategic Advisory Groups of Experts in immunization (SAGE), PHEs are recognized as one of the major shifts during the decade and a key driver of inequity in immunization access between and within countries in the region (22). With the end in sight of the DoV in 2020, there is need to take stock of immunization performance in countries experiencing PHEs. The evidence generated would advance the understanding that is critical in strengthening NIPs in the context of PHEs.

In as much PHEs have been recognized to have repercussions on NIPs, inadequate focus has been given on synthesizing evidence in PHE-affected settings in the WHO Africa region. Few studies have attempted to describe immunization in countries affected by PHEs, however, a majority are restricted to single types of PHEs, especially armed conflict and single immunization indicators (6, 11, 27). To the best of our knowledge, this will be the first study that aims to characterize NIPs in the WHO Africa region experiencing PHEs, using three different types of PHEs (i.e., armed conflicts, disease outbreaks, and disasters) and the DoV immunization targets to account for the performance of NIPs. Also, being a precursor descriptive study, NIP performance in countries affected by PHEs will be singularly analyzed without controlling for other third variables that may have influenced NIP performance. As such, the general scope of the study is limited in inferring a cause-effect relationship between PHEs and NIPs performance.

The primary intent of the study was to characterize the NIPs of countries within the WHO Africa region experiencing PHEs using immunization targets outlined for the DoV as proxy indicators. We found that PHEs were endemic during the entire study period and the performance of NIPs in the PHE-endemic countries was variable, although mostly suboptimal. Additionally, higher total PHE and armed conflict counts were associated with not achieving the immunization targets for ≥90% national DTP3 coverage and MNT elimination. Higher disaster counts were also associated with not eliminating MNT.

The endemicity of PHEs observed during the study period, agrees with other reports on the recurrent and diverse nature of PHEs experienced in the WHO Africa region (3, 36). While armed conflict and disasters were found to have the highest cumulative count in our study, contrary, trends were observed in the WHO Africa region, with a majority of reported PHEs being that of disease outbreaks (3, 36, 37). The discrepancy can be explained by findings from other studies done in similar settings, where disease outbreaks were noted to occasionally go unrecorded as they occur as a twin PHE, in the context of armed conflicts and disasters (2, 38).

Regardless of the immunization maturity level, the overall performance of NIPs in the PHE endemic countries was variable but predominantly suboptimal. The fluctuating and the low national DTP3 coverage rates below the WHO Africa region DTP3 coverage stagnation point are synonymous with DTP3 coverage reports in other NIPs in the region during PHEs (11, 21). As outlined by Grundy et al. in their study, other WHO Africa region countries like Nigeria and Somalia that have experienced constant civil unrest and were yet to benefit from the APHEF were reported to similarly have sub-optimal DTP3 coverage rates (6). Similarly, the high DTP vaccine drop-out; classified as ≥10% (24), recorded in some of the NIPs, concur with findings from a study by Mugali et al. (39) in Afghanistan where high DTP drop-out rates were associated with conflict and insecurity.

The introduction of the PCV and the Rotavirus vaccines into the NIPs of the study countries was high compared to the HPV vaccine. These findings are comparable to those in the region as 86, 76, and 8% of GAVI eligible countries had introduced the PCV, Rotavirus, and the HPV vaccines, respectively, by 2017 (40). Delay in HPV vaccine introduction has been attributed elsewhere to the poor adoption of life-course immunization, vaccine supply constraints, and pricing issues (16, 22) which stand exacerbated by PHEs (6). The outlier countries yet to introduce any of the three selected vaccines are potential key pointers to the contributing role PHEs play in delaying vaccine introductions into NIPs as raised by Grundy et al. in their study (6).

Despite the positive progress in NITAG establishment in the WHO Africa region (41), a non-consistent pattern in their existence and functionality simultaneously existed. Such inconsistent trends have been attributed in previous reports to the lack of political commitment and country ownerships of NIPs and the low NITAG financial investments, in general, and during PHEs (34, 41).

The elimination target for MNT was not met in countries with high counts of PHEs like South Sudan, the Central African Republic, Niger, Guinea, and Angola. The enlisted five countries constitute nearly 50% of the remaining global MNT elimination priority countries (42) and have similar trends with other MNT priority countries like Afghanistan and Yemen, where the presence of protracted PHEs has been blamed on delaying elimination (43).

Having higher armed conflict and total PHE counts were associated with not attaining the target for ≥90% national DTP3 coverage. These findings are comparable to those from studies conducted in similar contexts where armed conflicts were reported to be associated with poor immunization coverage outcomes (6, 11, 27). Conversely, while the Democratic Republic of Congo had the highest PHE count, its national DTP3 coverage was not the poorest. As described elsewhere, this finding in the Democratic Republic of Congo could be partly attributed to the humanitarian aid in the country (44). In addition, there have been recent specific plans developed by the government of the Democratic Republic of Congo in collaboration with technical and financial partners such as WHO and GAVI, The Vaccine Alliance to strengthen the NIPs in the country (45).

The findings further show that periods of higher counts of armed conflicts, disasters, and total PHEs were also associated with not eliminating MNT. Elimination of MNT in the WHO Africa region has been evasive to some extent, with most of the countries prioritized for MNT elimination being affected by PHEs (46, 47). In other PHE endemic contexts, where MNT elimination remains unattained, low tetanus vaccine coverage among women of reproductive age, unhygienic birth practices, delayed treatment, and inadequate MNT surveillance have been cited to delay progress (46, 48).

Higher counts of all the three types of PHEs and the total PHEs were not associated with meeting the immunization targets of having functional NITAGs or the introduction of new vaccines. The lack of consistency in the existence and functionality of NITAGs is not uncommon as observed in other PHE-prone contexts in the region (41). On the other hand, during PHEs, whereas the functionality of NITAGs may be compromised, the WHO recommends humanitarian immunization teams to utilize the unique expertise and local knowledge of existing NITAG members (17). For the target to introduce new vaccines, a possible caveat may exist in interpreting association, as within the scope of this study, only three vaccines were selected out of a pool of new vaccines. Conversely, we equally recognize that despite PHE endemicity, most of the case study countries had performed relatively well in this target which is also credited as one of the WHO Africa region DoV successes owing to political commitment and strong immunization investments (22). Arguably, such progressive performance noted in this DoV target, can offer a lesson; that the link between PHEs and immunization performance may not be always absolute.

In summation, it is imperative to note that central to the attainment of the discussed DoV targets and “health for all” as embodied under Sustainable Development Goal 3 (SDG 3) is the presence of peace and stability in a country which is a critical pillar to SDG 16 namely “peace justice and strong institutions” (49, 50). This will reciprocally ensure that every individual regardless of their background will have access to vaccines (50).

Our results should be interpreted in light of certain caveats. First, our study was limited to three broad types of PHEs, that may not be exhaustively representative of all types of PHE experienced in the study countries. Furthermore, it would have been useful to provide information on the duration of each of the PHEs assessed per country. However, owing to the retrospective and longitudinal design of this study, as well as the incomplete and inconsistent reporting of PHE data, the severity, and the duration of the PHEs, could not be analyzed within the scope of this study. It should be noted that PHEs often overlap in the real-world context, and it may be challenging to identify how a single PHE may have impacted the performance of immunization programs. Additionally, we may be unable to determine how previous PHEs experienced before the start of the study period in 2010 may have affected the NIPs in the selected countries.

Secondly, we used country-generated reports from the WHO/UNICEF JRF to abstract data on DoV immunization indicators. It is, possible that potential inaccuracies in the country data may have influenced the outcome of our study. However, this could not be avoided within the scope of this study. Data quality issues from country reports have been constantly highlighted as one of the major concerns by the WHO, SAGE in their annual DoV immunization reports (22, 26). Similarly, since our study used immunization indicators outlined for the DOV between 2010 and 2020 to assess NIP performance, analyzing pre-PHE years immunization data was beyond the scope of our study owing to differences in immunization goals between the pre-PHE period and the PHE period. Additionally, data on NIP immunization maturity was first availed in 2018 in the WHO Africa region (35), as such the study is unable to account for NIP maturity data for the period preceding 2018.

Lastly, while associations between the occurrence of PHEs and the performance of immunization programs were highlighted we cannot rule out with certainty the influence of other third variables on immunization program performance. It is also, worth noting several confounders may have affected the performance of NIPs in addition to PHEs which we were unable to account for, owing to the limited scope of the study in inferring a cause-effect relationship between PHEs and NIP performance. Similarly, it was not possible to account for emergency responses aimed at providing immunization services during PHEs. As such, our estimated results may represent a lower bound for the true effect of PHEs on immunization.

Future research investigations should address these limitations to broaden the scope of evidence on the interactions that exist between PHEs and immunization performance. We propose that future studies should further explore (1) how other types and grades of PHEs and the duration of PHEs may variably impact immunization performance, (2) immunization performance at the sub-national level using immunization data from localized communities where PHEs are recorded to occur, (3) how other third variables including NIP performance confounders may act together with PHEs to influence immunization performance, and (4) the analysis of PHEs and immunization performance in other WHO regions in comparison with the findings from the WHO Africa region.

PHEs are endemically present in the WHO Africa region and form part of the eco-system in which NIPs exist. With the goal of extending immunization to all individuals, countries experiencing PHEs within the WHO Africa region may be excluded from reaping the full benefits of immunization owing to unmet targets. Immunization performance in countries where PHEs are endemic are largely suboptimal and not at par with envisioned immunization targets for the DoV. As we transition to the Immunization Agenda 2030, PHEs like the COVID-19 pandemic, armed conflicts, and disasters are a major threat to NIPs. Therefore, priority should be given to developing evidence-based interventions to mitigate the impacts of PHEs on NIPs. Such interventions may include the commitment by governments in the WHO Africa region to strengthen the resilience of NIPs against PHE challenges by investing in PHE prevention and mitigation initiatives like the APHEF. Characterizing the performance of NIPs in PHE contexts is undoubtedly elemental in bridging the gap to equitable access to immunization for all populations, irrespective of where they live, thus enabling the collective achievement in shared goals like the DoV, SDG 3 and 16, and the Immunization Agenda 2030, thereby, enhancing regional health outcomes.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

BK conceived of the presented idea, provided critical feedback, and helped shape the manuscript. VC extracted and analyzed the data and wrote the manuscript. EA-D and ECH contributed to the development of the methods and coherence of the manuscript. All authors read, edited, and approved the final manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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