title: A systematic literature review of missed opportunities for immunization in low- and middle-income countries.
abstract: BACKGROUND
  Missed opportunities for immunization (MOIs) may contribute to low coverage in diverse settings, including developing countries.
  
  
  METHODS
  We conducted a systematic literature review on MOIs among children and women of childbearing age from 1991 to the present in low- and middle-income countries. We searched multiple databases and the references of retrieved articles. Meta-analysis provided a pooled prevalence estimate and both univariate and multivariate meta-regression analysis was done to explore heterogeneity of results across studies.
  
  
  RESULTS
  We found 61 data points from 45 studies involving 41,310 participants. Of the 45 studies, 41 involved children and 10 involved women. The pooled MOI prevalence was 32.2% (95% CI: 26.8-37.7) among children - with no change during the study period - and 46.9% (95% CI: 29.7-64.0%) among women of child-bearing age. The prevalence varied by region and study methodology but these two variables together accounted for only 12% of study heterogeneity. Among 352 identified reasons for MOIs, the most common categories were health care practices, false contraindications, logistic issues related to vaccines, and organizational limitations, which did not vary by time or geographic region.
  
  
  CONCLUSIONS
  MOI prevalence was high in low- and middle-income settings but the large number of identified reasons precludes standardized solutions.
authors.affiliation: Agence de Médecine Preventive, 164 Rue de Vaugirard, Paris 75015, France. Electronic address: shrutilion@gmail.com.
authors.forename: Shruti
authors.initials: S
authors.lastname: Sridhar
authors.affiliation: Agence de Médecine Preventive, 164 Rue de Vaugirard, Paris 75015, France.
authors.forename: Nadira
authors.initials: N
authors.lastname: Maleq
authors.affiliation: Agence de Médecine Preventive, 164 Rue de Vaugirard, Paris 75015, France.
authors.forename: Elise
authors.initials: E
authors.lastname: Guillermet
authors.affiliation: Agence de Médecine Preventive, 164 Rue de Vaugirard, Paris 75015, France.
authors.forename: Anais
authors.initials: A
authors.lastname: Colombini
authors.affiliation: Agence de Médecine Preventive, 164 Rue de Vaugirard, Paris 75015, France. Electronic address: bgessner@aamp.org.
authors.forename: Bradford D
authors.initials: BD
authors.lastname: Gessner
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003906:Developing Countries; D005260:Female; D006297:Health Services Accessibility; D006801:Humans; D007114:Immunization / Q000706:statistics & numerical data*; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D055815:Young Adult
keywords: Immunization; Meta-analysis; Missed opportunity; Systematic review; Vaccine; Vaccine hesitancy