Revaccination With Measles-Mumps-Rubella Vaccine And Infectious Disease Morbidity: A Danish Register-Based Cohort Study

Background. It has been hypothesized that revaccination with live vaccines is associated with reductions in off-target morbidity and mortality. We examined if revaccination with the live measles, mumps, and rubella vaccine (MMR) is associated with a lower rate of off-target infections.Methods. We performed a register-based nationwide cohort study that included 295 559 children born in Denmark from April 2004 to December 2010. The cohort were followed from age 47 months (1 month before turning age 4 years, which is the recommended age of the second MMR [MMR-2]) until age 60 months. In Cox regression, we estimated adjusted incidence rate ratios (aIRRs) of antibiotic prescriptions and hospital admissions for any infection comparing MMR-2 as most recent vaccine with not having MMR-2 as the most recent vaccine.Results. There was no association between MMR-2 and antibiotic prescriptions (aIRR, 1.01; 95% confidence interval [CI], 0.99-1.02). The aIRR for the association between MMR-2 and admissions for infection of any duration was 0.93 (95% CI, 0.88-0.98). For admissions for infection lasting 0 to 1 day, the aIRR was 0.97 (95% CI, 0.90-1.03) compared with the aIRR of 0.84 (95% CI, 0.74-0.95) for admissions for infection lasting 2 days or longer (test for equality of aIRRs, P = .039).Conclusions. In this study, revaccination with MMR appeared safe in relation to off-target infections and was associated with a lower rate of severe off-target infections. More studies of the possible association between revaccination with live attenuated vaccines and off-target infections are needed.