Assessing measles immunity among healthcare workers, a systematic review of peer-reviewed literature (2013-2023). Where do we go from here?

Background: Measles, a highly contagious disease, is experiencing a global resurgence, posing significant risks to healthcare workers (HCWs) due to occupational exposure. While previous studies have primarily evaluated HCW immunity using seroprevalence, no study has comprehensively assessed immunity by incorporating other widely used definitions, including documented evidence of immunity, natural immunity by birth cohort, and self-reported immunity. Method(s): A systematic review was conducted of HCW immunity surveillance studies published in English in peer-reviewed journals from January 2013 to February 2024. Data were extracted on (1) country, (2) author and year, (3) immunity assessment type, (4) study type, (5) data collection period, (6) immunity coverage results, (7) HCW count, (8) age ranges, (9) job roles, and (10) seroprevalence methodology and threshold values, where applicable. Result(s): A total of 98 studies were included, with immunity coverage ranging from 57.1 % to 99.2 %. Immunity assessments were based on seroprevalence, documented evidence, natural immunity by birth cohort, and self-reported immunity. Considerable heterogeneity was observed across study populations, immunity assessment methodologies, and situational contexts, including studies conducted during outbreaks. Studies included demonstrated that recall may underestimate immunity, as a high rate of seropositivity was observed among participants who did not remember being vaccinated or having measles. Conclusion(s): This study highlights a positive trend in HCW immunity coverage compared to previous findings. However, significant methodological variability in assessing measles immunity limits the ability to perform aggregated global analyses. Studies using only one method to assess immunity contribute to the perception of lower-than-expected immunity coverage, as this limited approach may not provide a complete or accurate picture of actual immunity levels. Future research should prioritize the development of standardized tools and methodologies to enable data harmonization and facilitate robust global immunity assessments. Copyright © 2025