Sero-prevalence of measles and rubella immunoglobulin G serum antibody in individuals 1-30 years old in England in 2018: implications for subsequent outbreaks prediction

PURPOSE: Measles outbreaks have occurred across England since mid-2023. We estimated measles and rubella antibody seroprevalence among individuals in 2018 in English regions outside London, and estimated the effective reproduction number (Re) for measles to predict the potential for outbreaks.

METHODS: Using validated enzyme-linked immunosorbent assays, anti-Measles and anti-Rubella IgG antibodies were measured in residual sera from 3758 1-30-year-olds born after introduction of measles-mumps-rubella vaccination who submitted samples to clinical laboratories outside London. The measles Re was calculated using seronegatives defined by the manufacturer's cutoff, mixture modelling, and vaccination coverage data.

RESULTS: Using the manufacturer's cutoffs, the overall proportion seronegative to measles was 9.2% (95% confidence interval 8.3-10.1), and 10.3% (9.4-11.3) had equivocal results. The respective estimates for rubella were lower at 5.2% (4.6-6.0) and 5.4% (4.7-6.1). For both viruses, equivocal proportions increased with age, consistent with antibody waning. Mixture modelling for measles identified a common seronegative distribution across age groups, with lower proportions seronegative than using the manufacturer's cutoff. Re for measles using the manufacturer's seronegative cutoff (~ 150 mille international units/mL) was 1.00, versus 0.38 and 0.51 using the mixture model and vaccination coverage, respectively.

CONCLUSIONS: Re for measles estimated from seroepidemiology using an antibody cut-off similar to that considered a correlate of protection for measles was a more accurate predictor of recent measles resurgences outside London than those estimated using mixture modelling of seronegatives or coverage data. Seroepidemiological studies are a useful adjunct to coverage data in monitoring population immunity and in predicting the potential for measles outbreaks.