Measles seropositivity in previously vaccinated individuals: a systematic review and meta-analysis

Background: With the resurgence of measles outbreaks globally it is important to understand how seropositivity induced by measles vaccination wanes over time. We aimed to measure the prevalence of measles seropositivity in vaccinated individuals and assess changes in antibody levels over time since vaccination. Method(s): We conducted a systematic review and meta-analysis by searching PubMed, Embase, Scopus, Web of Science, and Cochrane Library databases from January 1980 to April 2025 for studies reporting serological outcomes following measles-containing vaccination. The search criteria included clinical trials, cross-sectional studies, cohort studies, and case series with >=10 participants. The primary outcome was the proportion of vaccinated individuals seropositive for measles IgG antibodies. Meta-regression was performed to assess the relationship between seropositivity and time since vaccination. The study was registered with PROSPERO, CRD420251026672. Finding(s): The search identified 2348 unique records. Following title and abstract screening, 89 articles were selected for full-text review, of which 18 studies were included, encompassing 23,236 vaccinated individuals from 10 countries. Overall pooled proportion of seropositive individuals was 87.8% (95% Confidence Interval [CI] 83.9%-91.2%, I2 = 97.9%). Most individuals included in the analysis had received at least two doses of measles-containing vaccine, whereas evidence for single-dose recipients was limited. Single-dose recipients displayed a pooled seropositivity of 84.3% (95% CI, 71.6-93.9; 6 studies) and multi-dose recipients (individuals who received >=2 doses) exhibited 88.8% (95% CI, 84.4-92.6; 15 studies; p = 0.252 for between-group heterogeneity). Notably, only one study included solely single-dose recipients, highlighting that estimates for this group are based on limited data. The overall seropositivity declined with increased time between vaccination and serological assessment: 92.9% (95% CI, 84.3%-98.4%) within 10 years, 87.0% (95% CI, 70.4%-97.4%) at 11-15 years, 82.8% (95% CI, 67.8%-93.9%) at 16-22 years, and 81.9% (95% CI, 30.8%-100%) at >=23 years post-vaccination. Meta-regression suggested measles seropositivity declines at a rate of 0.48% per year in vaccinated individuals (beta = -0.048, 95% CI, -0.078 to -0.018; p = 0.002). Interpretation(s): Ten years after measles vaccination, vaccinated individuals displayed high seropositivity. The observed decrease in measles seropositivity in the years after vaccination may indicate waning humoral immunity. However, this systematic review and meta-analysis was unable to assess the relationship between seropositivity and measles infection rates, thus further investigation is needed. Funding(s): No funding was received for the study design, data collection, analysis, interpretation, writing of the manuscript, or the decision to submit for publication. Copyright © 2025 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license.