Measles immunity gaps in an era of high vaccination coverage: A serology study from Taiwan

Routine vaccination for children drastically reduces measles cases. Nonetheless, the global resurgence of measles since 2018 highlights the need for evaluating vaccine-induced immunity in an era of high vaccination coverage, especially in international travelers. This study aims to identify high-risk persons via analyzing the impact of age and different vaccination schedules on seroprevalence of measles in a country with high vaccination coverage, attempting to provide suggestions regarding pre-travel measles vaccination in highly immunized countries.

We retrospectively collected serological results of measles from Taiwanese travelers during 2008-2017 and middle-aged subjects from community during 2007-2009. Participants were classified by age groups and cohort based on the national immunization program: cohort I (pre-mass vaccination), cohort II (suboptimal measles vaccination), and cohort III (2-dose MMR in childhood). The effects of age group on seropositivity was shown by odds ratio (OR) with 95% confidence interval (CI) in a logistic regression model.

The overall measles seroprevalence was 74.5% (N = 1096, mean age = 31.7 ± 12.3 years), with adolescents having the lowest seropositivity (65.9%) and participants ≥50 years having the highest (89.4%). Seropositivity was significantly higher in cohort I (pre-mass vaccination) compared with the other 2 cohorts (P < 0.0001). The effect of aging on seropositivity was only significant in cohort II (OR = 1.84, 95% CI = 1.13-2.99, P = 0.014 for 30-39 years vs. 20-29 years).

Waning immunity to measles in adolescents and young adults is a dominant issue in highly vaccinated cohorts. Enhancing pre-travel vaccination against measles can effectively fill the immunity gaps in highly immunized countries.