Serological Protection After Routine Measles-Containing Vaccination Among Children Aged 1-5 Years in Low- and...

Background: Measles remains a major cause of morbidity and mortality among children in low- and middle-income countries (LMICs), despite widespread implementation of routine two-dose measles-containing vaccine (MCV) schedules. Serological assessment provides an objective measure of vaccine-induced immunity; however, evidence describing post-vaccination serological protection among children in LMICs remains fragmented and methodologically heterogeneous. Objective: To synthesize evidence on serological protection following routine two-dose MCV among children aged 1-5 years in LMICs and to identify determinants of immunity, methodological limitations, and evidence gaps relevant to immunization programmes. Methods: This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines and prospectively registered in PROSPERO (CRD420261300545). Literature searches were conducted in PubMed, MEDLINE, Scopus, Cochrane Library, CINAHL (EBSCO), and SciSpace on 21 January 2026. Two reviewers independently screened studies, extracted data, and assessed quality of evidence using Joanna Briggs Institute critical appraisal tools. Substantial clinical and methodological heterogeneity precluded meta-analysis; therefore, findings were synthesized narratively. Results: Eighteen studies met the eligibility. These studies were from 14 LMICs across four WHO regions (61.1% African Region, 27.8% Eastern Mediterranean Region, 5.6% each South-East Asia and the region of the Americas). Reported MCV seroprotection following completion of the two-dose schedule generally ranged from 30.6% to 100%, with the highest levels (87-100%), but with evident lower protection in specific settings, such as rural Pakistan (30.6%) and Ethiopia (40-54%) despite having documented vaccination records. Lower protection was consistently associated with undernutrition, human immunodeficiency virus (HIV) infection, incomplete or delayed vaccination, younger age at first dose, and weak programme performance. Considerable variability was observed in study design, vaccination schedules, laboratory assays (ELISA, PRNT, haemagglutination inhibition, and others), seroprotective thresholds, timing of antibody assessment, and participant characteristics. Risk of bias was largely moderate-to-high, and certainty of evidence ranged from low to very low. Conclusions: Routine two-dose measles vaccination generally provides substantial serological protection among children aged 1-5 years in LMICs. Nevertheless, methodological heterogeneity and geographical evidence gaps limit direct comparisons and reduce confidence in cross-study interpretation. Greater standardization of serological assessment and thresholds, harmonized reporting methods, and well-designed longitudinal studies are needed to strengthen the evidence base and support immunization policies aimed at achieving and sustaining measles elimination.