Adverse Events among Young Adults following a Third Dose of Measles-Mumps-Rubella Vaccine

Background: A third measles-mumps-rubella vaccine (MMR) dose (MMR3) is recommended in the United States for persons at increased risk for mumps during outbreaks. MMR3 is also likely given to persons who might have received two doses of MMR but lack documentation. Since MMR3 safety data are limited, we describe adverse events in persons receiving MMR3 in a non-outbreak setting.

Methods: Young adults with two documented MMR doses were administered MMR3. From two weeks before until four weeks after MMR3 receipt, participants reported daily on 11 solicited, common symptoms potentially associated with MMR. Weekly rate differences in post- vs. pre-vaccination (baseline) were evaluated by Poisson regression. Baseline rates were subtracted from post-vaccination rates of significantly different symptoms to estimate number and percentage of participants with excess risk for symptoms post-MMR3. Descriptive analyses were performed for three post-vaccination injection-site symptoms.

Results: The 662 participants were aged 18-28 years (median=20 years); 56% were women. Headache, joint problems, diarrhea, and lymphadenopathy rates were significantly higher post-vaccination vs. baseline. We estimate 119 participants (18%) reported more symptoms after MMR3 than pre-vaccination. By symptom, 13%, 10%, 8%, and 6% experienced more headache, joint problems, diarrhea, and lymphadenopathy, respectively, after MMR3. Median onset was days 3-6 post-vaccination; median duration was 1-2 days. One healthcare visit for a potential vaccination-related symptom (urticaria) was reported. Injection-site symptoms were reported by 163 participants (25%); median duration was 1-2 days.

Conclusions: Reported systemic and local events were mild and transient. MMR3 is safe and tolerable among young adults.

Keywords: MMR vaccine; adverse events; measles; mumps; rubella; third dose; vaccine safety; young adults.