Assessing measles immunity in individuals of childbearing age in Toronto, Ontario, Canada.

OBJECTIVES

Measles is a highly infectious virus with potentially serious complications. Infants too young to be vaccinated depend on maternally-derived, transplacentally-transferred antibodies for early protection. We aimed to identify factors influencing maternal measles immunity, and determine predictors of maternal susceptibility and infant immunity during the first year of life.

METHODS

Using a prospective cross-sectional study design, we collected data and samples from infant-mother pairs admitted to the Hospital for Sick Children between 2018 and 2020. Measles antibody titres were measured using the gold-standard plaque reduction neutralisation test.

RESULTS

We recruited 258 mothers aged 16-45 years, of whom 80.6% (95% CI: 75.8,85.4) had protective antibody levels. The proportion with protective antibodies was lowest among mothers <25 years at 67.9% (95% CI: 50.6,85.2), increasing to 100% (95% CI: 100.0,100.0) in those >40 years. Among the 233 individuals reporting vaccination status, 97.0% received at least one measles-containing vaccine.

CONCLUSIONS

Nearly one-fifth of mothers in our study were seronegative to measles, increasing to nearly one-third of mothers under 30 years. The higher susceptibility observed in younger individuals within a highly-vaccinated cohort may suggest waning humoral immunity. Further research is needed to understand the significance of the high proportion of seronegative individuals in younger age groups.