Infectious Disease
The Effect of Time Since First Dose of Measles-Mumps-Rubella (MMR1) Vaccine on Measles Immunity Archchun Ariyarajah* Archchun Ariyarajah Natasha S. Crowcroft Kevin A. Brown John Wang Jeff Kwong Shelly Bolotin
Background
Canada eliminated measles in 1998. However, immunity from the MMR vaccine can wane in elimination settings. Our study examines the impact of time since first dose (MMR1) on measles immunity.
Methods
We conducted a retrospective cohort study on 37,412 individuals in Ontario, Canada who underwent measles IgG antibody testing in 2014-16. Health administrative databases provided sociodemographic and health data. Vaccination was ascertained using physician billing claims data at 12-15 months of age. We measured measles antibody geometric mean concentration (GMC) and immunity defined as ≥275mIU/mL, with sensitivity analyses at ≥200mIU/mL and >120mIU/mL. We used multivariable negative binomial and logistic regression models with restricted cubic splines to estimate GMC and susceptibility, respectively, adjusting for confounders, across eliminated and endemic settings.
Results
Measles antibody GMC decreased substantially in the first 10 years post-MMR1 and decline slowed thereafter. In the cohort born in a measles elimination setting (data available 1-17 years), antibody GMC declined significantly from 2194.4mIU/mL (95%CI, 2038.9-2349.9) in year 1 to 992.4mIU/mL (95% CI, 951.7-1033.2) by year 10, and to 782.6mIU/mL (95% CI, 751.7-813.5) by year 17. At a ³275mIU/mL protection threshold, 25% (95% CI, 23-27%) were susceptible to measles by the seventeenth year, but at >120mIU/mL, susceptibility was 4% (95% CI, 3-5%). In the cohort born in a measles endemic setting (data available 15-25 years), antibody GMC declined from 821.7mIU/mL (95%CI, 802.6-840.9) in year 15 to 725.5mIU/mL (95%CI, 706.0-745.0) by year 25. At a ³275mIU/mL protection threshold, 28% (95% CI, 26-30%) were susceptible to measles by year 25, but at >120mIU/mL, susceptibility was 4% (95% CI, 3-5%).
Discussion
These results align with previous studies; however, susceptibility interpretation depends on the protection threshold. More research examining waning measles immunity in elimination settings is needed.