Reporting: The preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline (20) was used to report this meta-analysis.( Additional file 1 research checklist).
Searching strategies: The reviewers followed the PRISMA systematic review protocol as a reporting guideline for the PRISMA checklist, eligible studies for the study were selected in terms of titles, abstracts, and then full articles based on inclusion criteria. EMBASE, PubMed, Hinary, Google Scholar, Web of Science, Science Direct, and African Journals Online were systematically searched for articles that included Medical Subject Headings and free text languages. These databases were searched by using both controlled and free-text languages. In terms of free-text searches, the keywords included the following combination of terms: (Willingness, OR COVID-19 Vaccine OR Acceptance) AND Ethiopia. The controlled searches included the following Medical Subject Headings (MeSH) terms: “COVID-19 Vaccine Acceptance” and “Ethiopia” as recommended for each database. The search terms were used individually and in combination using “AND” and “OR” Boolean operators. The search was guided by PICO, population- a population that was intended to take the vaccine.
Inclusion and exclusion criteria: The following types of studies; study population comprised any age group, study outcome is willingness or intention to take vaccine, and study design is cross-sectional were included and articles published in English language were also included. However, qualitative studies were excluded from the systematic review and meta-analysis.
Outcome of interest: PICO: The population of the study was any age group and the outcome of interest was vaccine acceptance which thus was reported was “Are you willing to take COVID-19 Vaccine if available to you?” and measured as yes and no or willing versus unwilling. The level of vaccine acceptance was presented as frequency and percentage.
Screening and Data Extraction: Two reviewers (SAT and GGD) screened titles and abstracts against the inclusion criteria. Then an independent assessment was made for the full text of the articles by the two reviewers based on the predetermined inclusion and exclusion criteria. Inconsistencies between the reviewers were dealt with by a discussion and consensus of all the investigators. Data extraction was made by three authors (TM, GZM, and BGE) independently from a random sample of 20% of the papers to check consistency and found no variation across.
Study Quality Assessment: A structured data abstraction form was constructed in Microsoft excel. Attention was given to clarity of data, objective, study design, population, sample size, and proportion of vaccine acceptance. (Table 1) The methodological qualities of each article were assessed based on a modified version of the Newcastle-Ottawa Scale for the cross-sectional study. (21) Moreover, the Joanna Briggs Institute prevalence critical appraisal tool for use in the systematic review was used for the critical appraisal of the studies. (22)
Data Synthesis and Statistical Analysis: Data were extracted using a Microsoft Excel spreadsheet and imported to Comprehensive meta-analysis version3.0 software for further analysis. The pooled effect size with a 95% confidence interval of national COVID-19 vaccine acceptance was determined using a weighted inverse variance random-effects model. Heterogeneity across the studies was assessed using the I2 statistic, where 25, 50 and 75% represent low, moderate, and high heterogeneities consecutively. (23) A funnel plot and Beggs and Eggers tests were used to check the risks of publication bias. (24)