COVID-19 vaccine hesitancy: a systematic review of barriers to the uptake of COVID-19 vaccine among adults in Nigeria.

Background: Since the outbreak of coronavirus (COVID-19) disease was reported in 2019, huge human and material resources have been expended globally to combat the spread of the disease. Achieving herd immunity through mass vaccination remains an important strategy to adopt in the war against this disease since it is practically impossible for 60-70% of the population to achieve immunity through natural infection alone. Unfortunately, there have been widespread reports of COVID-19 vaccine hesitancy. This study aims to systematically review the literature to provide an up-to-date assessment of COVID-19 vaccine acceptance rates and also explore factors impacting COVID-19 vaccine hesitancy among adults in Nigeria. Main body of the abstract: A systematic search of indexed electronic peer-reviewed literature published from 2019 onwards was conducted in Science Direct, PubMed, ProQuest, and EBSCOhost databases and reported according to the PRISMA checklist and Synthesis without meta-analysis (SWiM) in systematic review reporting guidelines. Fifteen out of the 148 studies retrieved, met the inclusion criteria and these were critically appraised using the Centre for Evidence-Based Medicine Critical Appraisal checklist and Mixed Methods Appraisal Tool, version 2018. Basic descriptive statistic (percentage) was employed in the analysis of acceptance rates of the COVID-19 vaccine among various subgroups of adults in Nigeria, while a thematic analysis of the facilitators and barriers to the uptake of the COVID-19 vaccine in Nigeria was conducted. Acceptance rates ranging from 24.3% to 49.5% were observed across the four studies conducted among the high-risk populations in Nigeria, while the acceptance rates among the low-risk populations ranged from 26.0% to 86.2%. Themes such as socio-demographic factors, perception of risk factors, and concerns about the vaccine's safety and efficacy act interchangeably as facilitators and barriers to the uptake of COVID-19 vaccines, whereas political factors, conspiracy theories, and cost primarily act as barriers to vaccine uptake. Short conclusion: Substantial heterogeneity was observed in COVID-19 vaccine acceptance rates among adults in Nigeria. More than half of the studies reviewed reported acceptance rates below 60.0%. A multidisciplinary approach is recommended in engaging important stakeholders, to effectively address COVID-19 vaccine hesitancy in Nigeria.