1390 - Effectiveness of M-M-R^® II in outbreaks - a systematic literature review of real-world observational studies

Background: M-M-R^® II was approved in the US in 1978 and has been used globally for over 40 years . Widespread use of M-M-R^® II has resulted in important declines in incidence, morbidity, and mortality of measles, mumps, and rubella in the US and other countries. While vaccine immunogenicity and efficacy were established in multiple placebo-controlled trials of each vaccine component, there are limited studies on vaccine effectiveness (VE) of M-M-R^® II. This systematic literature review was conducted to summarize the VE of M-M-R^® II from real-world observational studies.

Methods: The literature search was conducted in Medline and Embase (through May 2019), and grey literature sources (through July 2019). All publications and findings in English language were screened by two independent reviewers. The study characteristics and VE results were extracted for each study.

Results: Ten full-text publications related to VE of M-M-R^® II were all identified from outbreak investigations and mainly in the US (n=8, sample size=318 - 20,496).
For measles outbreaks (n=4), VE ranged from 71% to 96% in different age groups. Among high school students, VE of ≥1-dose of M-M-R^® II was 94-96%. Among young adolescents, the incremental VE of ≥2-dose vs. 1-dose was 94.1%. When M-M-R^® II was used as post-exposure prophylaxis within 72 hours of exposure during an outbreak, the VE was 83.4% among children 6 months to 19 years old. In another study among infants 6-14 months old, VE was 71% against laboratory-confirmed measles.
 Among mumps outbreaks, the VE of 1-dose, 2-dose, and ≥1-dose M-M-R^® II compared to unvaccinated was 83-84%, 80-89%, 83-86% respectively. Three studies evaluating the effectiveness of a third dose of M-M-R^® II showed an incremental mumps VE of 60-88% for 3-dose vs. ≤ 2-dose. One study found that individuals who had received a 2^nd dose of M-M-R^® II ≥13 years (vs. < 13 years) before the outbreak had higher risk for contracting mumps.
 No study reported VE of M-M-R^® II in a rubella outbreak.

Conclusion: M-M-R^® II was found to be effective against measles and mumps during outbreaks. More effectiveness studies are warranted to further address questions on the relationship of VE and time since vaccination as well as the effectiveness of a third dose of M-M-R^® II for measles or mumps outbreak control.